One of the best ways to protect yourself from the common "fake" anti-virus malware that's all over the place is to spend a few moments getting to know your "real" anti-virus software.
Each anti-virus vendor handles things a bit differently, but it's basically "theme and variations". The screen shot to the right is what the AVG system status looks like. When you click on the AVG icon in the system tray (lower right of your screen), you'll see this screen. What you're looking for is a recent scan date, your last update (should be with in a few hours time window), and your license expiration date. You're also looking for green check marks for all the protection levels: Anti-Virus, Anti-Spyware, LinkScanner, Anti-Rootkit, e-Mail Scanner, License, Online Shield, Resident Shield, and the Update Manager. The goal is to recognize your system status when things are going well, so when if you get the dreaded "fake anti-virus" malware, you'll know it's fake.
If you get hit with the fake antivirus malware, here's what will happen. A pop-up will appear on your screen saying somthing like a threat was found and do you want to do a scan. In scome cases the pop up will ask you to purchase an anti-virus license. Don't do it! A good strategy is to remember your Windows shortcuts and use "ALT+F4" to close the window. Sometimes the pop-up looks like a Windows screen, but its actually a web page, and the "x" that would normally close the window is actually a link to do more harm. Use "ALT+F4" instead.
Spend a few moments today to look at what your anti-virus system status screen looks like, and you'll be better prepared for future "fake" threats.