Web sites that make their money from advertising usually subscribe to one or more advertising providers, such as Google Adsense. There are many others, including some that push ads that are really just scams.

One popular type of scam ad takes the form of a malware warning, presented to the unsuspecting user in a full-screen web page that seems to lock out the user completely. The example above (provided recently by a client) appears to be from Microsoft, generated by Windows anti-malware software, and it includes what is supposedly a Microsoft phone number.

In reality, this is just a web page, generated by Javascript from an advertisement on a shady web site. The full screen effect is produced by your web browser’s built-in full-screen view feature, triggered by the ad. These messages are not reporting the presence of malware; they are intended to scare you into calling a phone number. Messages of this type are categorized as ‘scareware‘.

A Google search for the phone number in the example above shows that it’s definitely associated with support scams.

These fake alerts vary in appearance and quality. Some are more convincing than others. Many are based on real malware warnings. You can see other examples by searching Google Images for ‘fake malware warning’.

It’s important to understand that legitimate anti-malware software won’t ‘lock’ your computer when it detects malware, and it won’t insist that you call a phone number.

If you see one of these scary-looking screens, don’t panic. Obviously, don’t call the phone number shown on the screen. Nothing good will come from that. Try pressing the F11 key on your keyboard. This is the near-universal key that toggles full screen view in web browsers. If it is just a web page, pressing F11 will reveal your web browser’s user interface, and you should regain your bearings immediately. Close the tab, and/or close the browser.

Also, please reconsider visting any web site that’s operated by people who care so little for visitors that they are willing to inflict this kind of dangerous garbage on them, albeit indirectly.

More useful information about this from the Safety Detectives site.