As the US-CERT (United States Computer Emergency Readiness Team) points out, if you are just browsing on the Internet, and all of a sudden you are getting pop-ups that supposedly scan your computer and report problems that can only be remedied by downloading the software that they oh-so helpfully offer right away (in the form of download dialogs), DON’T!

These programs call themselves “Antivirus XP 2008? or something helpful like that, but unless you actually ASKED to download an application, you should treat this with the utmost care and not install it. (If you are using a Mac, you could still get the pop-ups, which is funny when they mimic Windows applications on your OS X desktop; plus, the apps wouldn’t run on the Mac side anyway.)

The golden rule is always: don’t download any files you haven’t specifically asked for, let alone run them. Make sure you have current, active and updated protection, from a reputable source. More information, as well as a video that shows how such an attack can look like can be found here.