I recently found a Virus. It's called System Tool. How it works is you download it from a random website and is called a random filename, such as AFL.exe. When you run it it installs all the files deep into your files. It lags the hell out of your computer while scanning. It automatically starts a scan when it starts up. There are setting for it that allows it to stop scanning, starting up, and everything but you have to buy a key first. While you have it it doesn't allow you to open up ANY programs. It won't even let you open up the task manager to end it. If you try and open up a program it closes it and gives you a message saying it is infected and asks you to remove it. Overall one of the worst viruses out there. Considering this is the only real one I've had.
Just a heads up, 99% of the anti-virus software is a virus.
Also if you do download it, you can't open up the remove programs window because it isn't listed. If you find the files and delete them, they are still running. The only way to remove it is system restore.