Browser Hijacker

What is a Browser Hijacker?

April 07, 2025

Browser hijackers are malicious software entities that modify browser settings without user authorization, accounting for 19.7% of all PUA (Potentially Unwanted Application) detections in 2023-2024 according to Microsoft Security Intelligence data. These specialized threats operate by altering DNS settings, modifying browser preferences files, installing unauthorized extensions, and manipulating registry values to maintain persistence. Current detection rates show browser hijackers affecting over 87 million devices worldwide, with Chrome and Edge browsers experiencing the highest infection rates at 62% and 23% respectively.

Technical Definition and Classification

Browser hijackers are unauthorized software components that programmatically modify critical browser configurations and settings. According to the MITRE ATT&CK framework, these threats primarily utilize techniques T1176 (Browser Extensions), T1112 (Modify Registry), and T1059.001 (PowerShell) for execution and persistence. From a technical standpoint, browser hijackers manipulate browser settings files, extension databases, and system-level configuration parameters.

Browser hijackers typically implement the following technical mechanisms:

• DOM manipulation: Injection of unauthorized JavaScript to modify webpage content in real-time
• HTTP header interception: Modification of HTTP requests to inject tracking parameters
• Preference file manipulation: Direct modification of browser preference files (prefs.js in Firefox, Preferences in Chrome)
• API hooking: Interception of browser API calls to alter functionality
• Browser process injection: Memory-resident code that modifies browser behavior without filesystem artifacts

In Microsoft's threat classification taxonomy, browser hijackers are categorized as "Browser Modifiers" (ID: 8000000) within their threat protection system. They are technically classified as PUAs rather than true malware, as they typically don't implement encryption, data exfiltration via command and control channels, or system compromise techniques found in advanced threats.

Current Prevalence and Statistical Data

Recent telemetry data reveals significant trends in browser hijacker prevalence and distribution:

• According to Microsoft's Security Intelligence Report, browser hijackers account for 19.7% of all PUA detections globally
• Chrome Browser remains the primary target (62.3% of detections), followed by Edge (23.4%), Firefox (10.1%), and Safari (4.2%)
• Browser hijacker distribution increased by 17.3% in 2023 compared to 2022, with a 22.5% increase in mobile browser targeting
• Average dwell time (period between infection and detection) is 42 days for browser hijackers
• Software bundling remains the primary distribution vector (58.4%), followed by drive-by downloads (42.1%)
• 94.2% of browser hijackers implement some form of data collection functionality

Browser extension stores continue to be significant vectors for hijacker distribution, despite increased security measures. Chrome Web Store removed 2,485 malicious extensions in Q4 2023, of which 36.7% were classified as browser hijackers. Firefox Add-ons marketplace documented the removal of 743 extensions with hijacking capabilities during the same period.

Hijacker Classification and Technical Taxonomy

Current browser hijacker threats can be classified according to their technical implementation and attack methodology:

1. Search Engine Redirectors

These threats modify the DefaultSearchProvider registry keys or preference files to redirect search queries. They typically intercept HTTP/HTTPS requests to legitimate search engines and inject tracking parameters or completely redirect the traffic through proxy servers. Technical indicators include modifications to:

• For Chrome: %LOCALAPPDATA%\Google\Chrome\User Data\Default\Preferences within the "default_search_provider" JSON object
• For Firefox: %APPDATA%\Mozilla\Firefox\Profiles\*.default\prefs.js modifying the "browser.search.defaultenginename" value
• For Edge: HKEY_CURRENT_USER\SOFTWARE\Microsoft\Edge\SearchScopes registry keys

2. DNS Manipulators

Advanced hijackers that operate at the network level by modifying DNS settings. These implement their attack by changing system DNS server addresses or modifying the hosts file. Technical indicators include:

• Modifications to %WINDIR%\System32\drivers\etc\hosts file with suspicious redirects
• Changes to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\NameServer registry values
• Alteration of network adapter DNS settings via PowerShell or WMI
• Implementation of local DNS proxy services listening on 127.0.0.1:53

3. Proxy Configurators

These hijackers implement HTTP/HTTPS proxies that intercept all browser traffic. They modify proxy settings at system or browser level to redirect traffic through malicious proxy servers. Technical indicators include:

• System proxy modifications in HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\ProxyServer
• Chrome proxy settings changes in %LOCALAPPDATA%\Google\Chrome\User Data\Default\Preferences within the "proxy" section
• Creation of PAC (Proxy Auto-Configuration) files and setting AutoConfigURL registry values
• Installation of proxy services running on localhost with ports in the 8000-9000 range

4. Extension Injectors

These threats forcibly install browser extensions, either through the official stores or via direct filesystem manipulation. Technical indicators include:

• Unauthorized extensions in %LOCALAPPDATA%\Google\Chrome\User Data\Default\Extensions
• For Firefox, suspicious XPI files in %APPDATA%\Mozilla\Firefox\Profiles\*.default\extensions
• For Edge, unauthorized extensions in %LOCALAPPDATA%\Microsoft\Edge\User Data\Default\Extensions
• Modification of extension-related registry keys to bypass signature verification

5. Browser Process Modifiers

The most sophisticated category that implements code injection techniques to modify browser processes in memory. These threats often bypass disk-based detection by operating entirely in RAM. Technical indicators include:

• Unusual DLL loading in browser processes detected via Process Explorer or Process Monitor
• Unexpected browser process child processes or command line parameters
• Browser process memory modifications detected through memory forensics
• Code injection events captured in EDR (Endpoint Detection and Response) logs

Technical Indicators of Compromise

Browser hijackers leave specific technical artifacts that can be identified through system examination. The following artifacts indicate potential browser hijacker presence:

Filesystem Indicators

• Unexpected files in browser profile directories with recent modification timestamps
• Modified browser preference files with unauthorized search engine configurations
• Suspicious executable files in system temporary folders with random names
• PAC (Proxy Auto-Configuration) files typically stored in %TEMP% or %APPDATA% directories
• Browser extension files (.crx, .xpi) located outside the standard extension directories
• JSON preference files containing references to unknown search providers

Registry Indicators

• Modified values in HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run for persistence
• Changes to HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\SearchScopes
• Alterations to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Browser Helper Objects
• New HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_DLLs entries
• Modifications to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\system\EnableLUA to disable UAC

Network Indicators

• Unexpected DNS queries to domains with low prevalence or reputation scores
• HTTP(S) requests containing specific tracking parameters (e.g., utm_source= with suspicious values)
• TLS connections to recently registered domains or IP addresses
• Unusual port activity on localhost (common proxy ports: 8080, 8118, 9050, 3128)
• Periodic "heartbeat" connections to command and control servers
• DNS requests with high entropy domain names (potential DGA - Domain Generation Algorithm)

Process Indicators

• Browser processes with unusual command line parameters
• Multiple browser instances running simultaneously with different user profiles
• Unfamiliar processes with names similar to legitimate system processes
• Browser processes with unexpected child processes
• High resource utilization from browser processes even when idle

Technical Detection Methodologies

Modern browser hijacker detection requires multi-layered technical approaches combining static and dynamic analysis:

Static Analysis Techniques

The following command-line tools and parameters can be used to detect browser hijacker artifacts:

# Check Chrome preference files for unauthorized search providers
findstr /C:"default_search_provider" "%LOCALAPPDATA%\Google\Chrome\User Data\Default\Preferences"

# Examine Edge browser extension installation records
dir /s "%LOCALAPPDATA%\Microsoft\Edge\User Data\Default\Extensions"

# Review Firefox prefs.js for unexpected search engine configurations
findstr /C:"browser.search" "%APPDATA%\Mozilla\Firefox\Profiles\*.default\prefs.js"

# Analyze startup registry keys for persistence mechanisms
reg query "HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /s

# Check system proxy configuration
reg query "HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings" /v ProxyServer

Dynamic Analysis Methods

• Process monitoring: Use Process Monitor to capture browser process activities, filtering for registry operations, file system operations, and network connections
• Network traffic analysis: Implement Wireshark with display filters like http.request.uri contains "search?" to identify search redirection
• DNS monitoring: Set up DNS query logging to identify unexpected DNS requests using tools like dnscap or Microsoft Network Monitor
• Browser debugging: Use browser developer tools to monitor HTTP requests, specifically examining request headers and redirection chains

Advanced Detection Scripts

The following PowerShell script can be used to check for common browser hijacker indicators:

# PowerShell script to detect browser hijacker artifacts
$chromePrefs = "$env:LOCALAPPDATA\Google\Chrome\User Data\Default\Preferences"
$firefoxProfiles = Get-ChildItem "$env:APPDATA\Mozilla\Firefox\Profiles\*.default" -ErrorAction SilentlyContinue
$edgePrefs = "$env:LOCALAPPDATA\Microsoft\Edge\User Data\Default\Preferences"
$hostsFile = "$env:windir\System32\drivers\etc\hosts"

Write-Host "Checking for browser hijacker indicators..." -ForegroundColor Yellow

# Check Chrome preferences
if (Test-Path $chromePrefs) {
    $prefs = Get-Content $chromePrefs -Raw | ConvertFrom-Json
    Write-Host "Chrome search engine: " $prefs.default_search_provider.name
    if ($prefs.default_search_provider.name -notmatch "Google|Bing|Yahoo|DuckDuckGo") {
        Write-Host "Suspicious search engine detected in Chrome!" -ForegroundColor Red
    }
}

# Check Firefox preferences
foreach ($profile in $firefoxProfiles) {
    $prefsFile = Join-Path $profile.FullName "prefs.js"
    if (Test-Path $prefsFile) {
        $searchEngine = Select-String -Path $prefsFile -Pattern "browser\.search\.defaultenginename"
        Write-Host "Firefox search engine: " $searchEngine
        if ($searchEngine -notmatch "Google|Bing|Yahoo|DuckDuckGo") {
            Write-Host "Suspicious search engine detected in Firefox!" -ForegroundColor Red
        }
    }
}

# Check hosts file for suspicious entries
$hosts = Get-Content $hostsFile
foreach ($line in $hosts) {
    if ($line -match "^\d+\.\d+\.\d+\.\d+\s+(?!localhost|broadcasthost)") {
        Write-Host "Suspicious hosts file entry: $line" -ForegroundColor Red
    }
}

# Check proxy settings
$proxySettings = Get-ItemProperty "HKCU:\Software\Microsoft\Windows\CurrentVersion\Internet Settings"
if ($proxySettings.ProxyEnable -eq 1) {
    Write-Host "System proxy enabled: $($proxySettings.ProxyServer)" -ForegroundColor Yellow
}

Technical Removal Procedures

Effective browser hijacker removal requires a systematic approach addressing both browser and system-level components. The following technical procedures provide comprehensive remediation:

Command-Line Removal Techniques

Chrome Remediation Commands

# Reset Chrome settings via command line
"%PROGRAMFILES(X86)%\Google\Chrome\Application\chrome.exe" --reset-profile-settings

# Force uninstall extensions via registry
reg delete "HKCU\Software\Google\Chrome\Extensions" /f

# Clear Chrome preferences (forces reset on next launch)
del "%LOCALAPPDATA%\Google\Chrome\User Data\Default\Preferences"

# Rebuild Chrome Secure Preferences
del "%LOCALAPPDATA%\Google\Chrome\User Data\Default\Secure Preferences"

Firefox Command-Line Remediation

# Safe mode launch to disable extensions
"%PROGRAMFILES%\Mozilla Firefox\firefox.exe" -safe-mode

# Reset Firefox from command line
"%PROGRAMFILES%\Mozilla Firefox\firefox.exe" -ProfileManager

# Remove all Firefox extensions
del /s /q "%APPDATA%\Mozilla\Firefox\Profiles\*.default\extensions\*.*"

System-Level Removal Commands

# Reset system proxy settings
netsh winhttp reset proxy

# Clear DNS cache to remove poisoned entries
ipconfig /flushdns

# Reset hosts file to default (requires elevation)
echo 127.0.0.1 localhost > %WINDIR%\System32\drivers\etc\hosts
echo ::1 localhost >> %WINDIR%\System32\drivers\etc\hosts

# Check for and remove persistent scheduled tasks
schtasks /query /fo LIST /v | findstr /i "suspicious_task_name"
schtasks /delete /tn "SuspiciousTaskName" /f

Registry Remediation Techniques

The following registry locations should be examined and cleaned to remove hijacker persistence:

• Run keys: HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run and HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
• Browser helper objects: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Browser Helper Objects
• Internet settings: HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings
• Winlogon entries: HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Userinit
• Group Policy browser settings: HKLM\SOFTWARE\Policies\Google\Chrome or equivalent for other browsers

Browser-Specific Technical Procedures

Google Chrome

1. 1. Navigate to chrome://settings/resetProfileSettings to access the built-in reset functionality
2. 2. Examine chrome://extensions for unauthorized extensions, noting their IDs for filesystem verification
3. 3. Check chrome://policy to identify any administrative policies enforcing unwanted settings
4. 4. Verify Extension Installation Source in %LOCALAPPDATA%\Google\Chrome\User Data\Default\Extensions
5. 5. Compare extension IDs with Chrome Web Store database to confirm legitimacy

Mozilla Firefox

1. 1. Launch Firefox in Safe Mode using firefox.exe -safe-mode to temporarily disable extensions
2. 2. Navigate to about:support and click "Refresh Firefox" for built-in reset functionality
3. 3. Examine about:config filtering for "browser.search" to identify search engine manipulations
4. 4. Check about:addons for suspicious extensions, noting their IDs
5. 5. Verify XPI files in profile directory against known malicious extension signatures

Microsoft Edge

1. 1. Navigate to edge://settings/resetSettings to access reset functionality
2. 2. Check edge://extensions for unauthorized extensions
3. 3. Examine edge://policy for administrative settings enforcing configurations
4. 4. Verify Edge extension installations in %LOCALAPPDATA%\Microsoft\Edge\User Data\Default\Extensions
5. 5. Inspect Edge preferences file for unexpected proxy or search engine configurations

For browser hijackers employing advanced persistence techniques, manual removal may be insufficient. In these cases, specialized tools with behavioral detection capabilities provide more effective remediation.

Browser Hijacker Persistence Techniques

Modern browser hijackers implement sophisticated persistence mechanisms to survive system reboots and removal attempts. Understanding these techniques is essential for effective remediation:

Registry-Based Persistence

Scheduled Task Persistence

Browser hijackers frequently create scheduled tasks to maintain presence or re-download components. Common patterns include:

• Tasks with random names containing legitimate-looking Microsoft or browser vendor identifiers
• Task triggers set to user logon, system idle state, or specific time intervals
• Actions typically invoking PowerShell or WScript with encoded commands to evade detection
• Task XML definitions containing obfuscated command parameters

Detection command: schtasks /query /fo LIST /v | findstr /i "powershell wscript cmd"

WMI Event Subscription Persistence

Advanced browser hijackers use WMI event subscriptions for fileless persistence. Typical implementation includes:

• Event filters monitoring for system or user events
• Event consumers executing PowerShell or other scripting engines
• Binding classes connecting filters to consumers

Detection command: wmic /NAMESPACE:"\\root\subscription" PATH __EventConsumer GET /format:list

Browser-Specific Persistence

Each browser implements its own storage mechanisms that hijackers target for persistence:

Advanced hijackers employ file system ACL modifications to prevent deletion of their components, requiring command-line tools to reset permissions before removal:

# Reset permissions on a protected file
icacls "C:\suspicious\file.exe" /reset /T

# Take ownership of protected registry key
reg.exe ADD "HKLM\SOFTWARE\Policies\Google\Chrome" /reg:64 /f

Technical Prevention Strategies

Implementing robust technical controls can significantly reduce browser hijacking risks. The following configuration settings and technical measures provide effective protection:

Group Policy Settings (Enterprise Environments)

# Chrome GPO settings to block extension installation
Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Google\Chrome]
"ExtensionInstallBlocklist"=dword:00000001
"ExtensionInstallWhitelist"="whitelist_extension_id1,whitelist_extension_id2"

# Block registry modifications to proxy settings
[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\CurrentVersion\Internet Settings]
"ProxySettingsPerUser"=dword:00000000

Browser Hardening Settings

Network-Level Protection

• DNS filtering: Implement DNS security services (Quad9, Cloudflare, or Cisco Umbrella) that block malicious domains
• HTTPS inspection: Deploy TLS inspection at the perimeter to detect malicious redirects and connections
• Network monitoring: Configure NetFlow analysis to detect unusual connection patterns
• Proxy categorization: Implement URL categorization to block uncategorized or newly registered domains

System Hardening Techniques

# PowerShell script to harden system against browser hijackers
# Set Application Control policies
Set-ProcessMitigation -System -Enable DEP,ASLR,ForceRelocateImages,RequireInfo

# Configure Windows Defender to block PUAs
Set-MpPreference -PUAProtection Enabled

# Enable Attack Surface Reduction rules
Set-MpPreference -AttackSurfaceReductionRules_Ids BE9BA2D9-53EA-4CDC-84E5-9B1EEEE46550 -AttackSurfaceReductionRules_Actions Enabled

# Block executable files from running unless they meet prevalence, age, or trusted list criteria
Add-MpPreference -AttackSurfaceReductionRules_Ids 01443614-cd74-433a-b99e-2ecdc07bfc25 -AttackSurfaceReductionRules_Actions Enabled

# Block JavaScript and VBScript from launching downloaded executable content
Add-MpPreference -AttackSurfaceReductionRules_Ids D3E037E1-3EB8-44C8-A917-57927947596D -AttackSurfaceReductionRules_Actions Enabled

For comprehensive protection against browser hijackers and other unwanted programs, deploy solutions with real-time monitoring and behavioral detection capabilities. Modern protection approaches focus on identifying suspicious behavior patterns rather than relying solely on signature-based detection.

References

• Microsoft Security Intelligence: Browser Modifier Threats
• CISA Advisory on Browser Extension Security
• Technical Analysis of Clarity Tab Browser Hijacker

Frequently Asked Questions