Real Browser Extension vs Malicious Extension
How to tell a trustworthy browser extension from a malicious one designed to steal data or hijack your browser.
Last reviewed: 1 June 2026
Malicious browser extensions are a particularly effective attack vector because they operate inside your browser with access to every page you visit, every form you fill in, and every session cookie you hold. They may arrive as convincing fakes of popular tools, as an extension that was legitimate until it was sold to a new developer who turned it malicious, or as something promoted through a deceptive ad. A well-designed malicious extension can silently harvest banking credentials, inject ads, modify search results, or redirect you to phishing pages — all while appearing completely functional. Scrutinising permissions before installing is the most effective prevention.
Side-by-side comparison
| Real browser extension | Malicious extension | |
|---|---|---|
| Source | Installed from the official browser extension store | Installed from a third-party website or via a deceptive ad |
| Permissions | Requests only the permissions necessary for its stated function | Requests broad permissions — all sites, read all data — unrelated to its purpose |
| Developer history | Developer verifiable; consistent update history in the store | Anonymous developer; very new or irregular update history |
| Reviews | Substantial, varied reviews with substantive feedback | Few reviews, overly positive bulk reviews, or no reviews |
| User count | User count consistent with the tool's age and niche | Very low user count for a broadly promoted tool |
| Behaviour | Performs only the function advertised; no unexplained network activity | Unexpected behaviour: modified search results, redirects, new ads |
| Post-install changes | Only affects the specific sites or functions it was designed for | Changes your default search engine, homepage, or injects content broadly |
Common red flags
- Extension installed from a website rather than the official browser store
- Permission request for 'read and change all data on all websites'
- Developer with no history or a very recently created account
- Promoted heavily through ads or pop-ups rather than the extension store
- After installation, unexpected changes to search results, homepage, or new ads appear
- Extension requests access to your clipboard, camera, or location when unneeded
Verification steps
- Only install extensions from the official browser extension store for your browser
- Read the permissions list carefully before accepting — question any broad access that doesn't match the tool's purpose
- Search the extension name plus 'malicious' or 'review' before installing
- Audit your installed extensions periodically and remove any you no longer use or don't recognise
- Check for any unexpected changes to browser behaviour after installing new extensions
What not to do
- Don't install extensions from links in ads, emails, or pop-ups
- Don't grant permissions that seem disproportionate to the tool's stated purpose
- Don't ignore post-install changes to your browser's behaviour
- Don't assume an extension is safe because it has worked correctly for some time — some turn malicious after ownership changes
A safe response
Remove the suspected extension immediately through your browser's extension manager. Change passwords for accounts accessed during the period the extension was active, particularly for banking and email. Run a scan with reputable security software and monitor your accounts for unusual activity.
Frequently asked questions
Can an extension really read my banking passwords?
Yes. An extension with broad site permissions can read the content of every page you visit, including the text you type into login forms. This is why reviewing permissions before installing is critical.
Is an extension safe if it has a lot of users?
A large user count from a known developer on an established extension is a positive signal, but not a guarantee. Extensions have turned malicious after being sold or compromised. Periodic audits of your installed extensions are worthwhile regardless.
How do I know if an extension is already doing something harmful?
Signs include unexpected ads appearing on normally ad-free pages, your default search engine changing without your action, slow browsing, or receiving phishing messages that reference details only your browser session would know. Remove suspicious extensions promptly.