Scareware is the latest computer attack. It is actually a spinoff of the famililiar phishing attacks that used bait to hook a victim into visiting their infected website. Scareware on the other hand tricks you into installing rogue antivirus software by "alerting" you that your computer might be infected. Let me ask, if you don't have security software installed on your computer, how did the "alert" magically appear? If you do have a security product installed that identifies and blocks malicious software, why did it tell you to buy or download more software to clean the alleged infection? Become familiar with what your security software's alerts look like so you can recognize the fake pop-ups. When one of these fake alerts apears, the safest thing to do is to press and hold the following three keys: Ctrl Alt Delete. A Windows security window will open, click on "Task Manager" then highlight and end task on the application that is causing the fake alert message.
Below are screen shots of 3 security alerts. All of these are fake, any of these if installed will cause system instability and are very difficult to remove. There are many more out there, become familiar with the type of security protection you have installed on your computer and what it looks like, so you are not "scared" into installing an application that will harm your system.