A warning appears in the corner of the desktop: problems found, act now. Its colours resemble a security product, but the small sender label names a website. A website notification is a message the site was allowed to send; the alarming wording is not evidence that it scanned your computer.
Read the sender before the headline
Look for the browser name and website address shown by the notification. Do not use its “fix” button, download a suggested cleaner or call a number inside it. Open the browser’s settings yourself.
Notifications are different from advertisements inside a page and from pop-up windows. Blocking pop-ups alone may leave a website’s notification permission untouched. If the sender is an installed app instead, review that app’s notification settings rather than searching for a site that is not there.
Remove the site’s permission
In desktop Chrome, open Settings, then Privacy and security, Site settings and Notifications. Review the allowed sites and block the unwanted sender. Chrome also lets you add an address directly to the list of sites not allowed to send notifications.
Match the address carefully. A familiar logo does not tell you which site sent the message. With several browser profiles, check the profile that received it.
Google says Chrome can block misleading notifications and review old permissions automatically. You can still inspect the list yourself; there is no need to wait for that review.
Check the result without revisiting the site
Confirm that the sender is now blocked and dismiss the old notification. A notice already visible is not a useful test of whether future messages are allowed.
For example, a one-time visit to a wallpaper site may have left an unwanted notification permission. Removing that permission addresses the messages. It does not prove that every part of the computer is clean. If you also downloaded or ran something, open your usual security application independently and investigate that separate event.