I had the "I Love You" virus back in 2001. Norton Anti Virus was disabled after I inastalled a program, I forgot to turn it back on.
I clicked on a MP3, but I failed to realize the extension, example: Rolling Stones - Paint It Black.mp3.vbs
I clicked on it and the hard drive went nuts, then Outlook popped up, I don't use Outlook, I powered the computer off.
In 30 seconds it renamed all my MP3's and over 10 thousand photos for work, they were useless.
Luckily I had a back up image I took of the drive on another drive that was off at the time. I restored the back up image and ran a virus scan to make sure nothing was hiding anywhere. I was back up and running in a couple hours, that included the scan times.
That was a scary one.
Always back up your hard drive, imaging like Aconis True Image is the way to go.