Why do fake security warnings keep appearing in my browser?

No. A warning displayed in a browser is not, on its own, proof that your device is infected. Some websites imitate pop-up windows or show an animated fake scan; Mozilla advises not to click misleading popups. [S2] The message could also be a site notification or relate to an add-on, so it helps to identify how it appears before deciding what to check.

For now, don’t click buttons or links inside the alarming message. Note whether it appears only on one webpage, arrives when the browser is open but that page is gone, or appears across different pages. Those observations may help you choose what to check, but they do not establish whether the device has malware.

A site notification is a browser permission: in Firefox, web push notifications require permission from the site, and Mozilla provides steps to review, block, or remove a site’s permission. [S1] That means a notification from a site is not, by itself, proof of infection. The supplied guidance is Firefox-specific; it doesn’t describe every browser or every kind of popup.

If you suspect a site notification, check the browser’s site-notification permissions and look for a site you don’t want to hear from. In Firefox, use Mozilla’s instructions to review or remove that site’s permission. [S1] If the message appears as part of a webpage, leave the page without interacting with the warning. A page can imitate a pop-up, so its appearance alone doesn’t verify that it is a genuine security alert. [S2]

An unwanted add-on is another possibility to check, not a conclusion about what caused the warning. Mozilla recommends checking for unwanted add-ons and removing them when troubleshooting Firefox issues that may involve malware. [S2] The source doesn’t establish that an add-on is responsible in your case, or that removing one will resolve the warning.

Review the browser’s installed add-ons and consider whether anything is unfamiliar or unwanted. Don’t assume what an add-on does based on a scary popup. If you use Firefox, consult Mozilla’s troubleshooting guidance for its recommended checks. [S2] These sources do not provide menu instructions for other browsers, so use that browser’s own help guidance rather than following buttons supplied by the warning.

Use this short observation note before changing anything. The example is hypothetical; replace the bracketed parts with what you actually observe:

1. Where it appeared: [inside a webpage / as a notification / uncertain]
2. When it appeared: [while viewing a particular site / after leaving it / other]
3. Site or page, if known: [site name or “unknown”]
4. What it asks me to do: [brief description; don’t follow its links]
5. Check to try: [review site notification permission / review add-ons / neither yet]

Then match the observation cautiously. If you suspect a site notification, review the relevant site permission; Firefox lets you review, block, or remove notification permissions. [S1] If it looks like a webpage imitating a pop-up or fake scan, don’t click it. [S2] If you suspect an add-on, review installed add-ons rather than treating the warning itself as proof. [S2]

These checks help organize what you’re seeing; they are not a malware scan or a diagnosis. The supplied sources cover Firefox guidance and do not establish what caused a particular warning or whether a device is infected.