A good guess would be using the computer as a zombie. Using the persons computer to send out millions of garbage email, faxes, etc. The bot army wants you!

I'm sure Bob's computer runs faster than it ever did.  My neighbor's computer did.  He fell for it, let a random caller take control of his computer.  I found out about it about a month later and told him its a scam.  He took the computer to a local repair place.  Those folks discovered that the scammer had turned-off the anti-virus.  They never could find anything that the scammer had installed so they replaced the computer.  Also, just to be safe, they changed all of their bank account numbers.    

I'd still like to know what the scammers did with that computer at night when it wasn't being used.  I suspect maybe DOS attacks or mass spamming.

Of course they did, Bob.  Brother, you must think Americans are very stupid.

You might rope someone in if warnings about this scam didn't show up on the internet and in the newspapers almost weekly.  

Get a real job, Bob.  Or Kumar, or whatever your real name is.

May be sometimes it is too hard to make someone understand on phone, they say it is for quick resolution !

Suuuuure they did!
PEOPLE! Never let a caller (or an e-mailer) coerce you into letting them gain access into your computer. EVER! It is invariably a SCAM!
It's that simple. End of story..
Live Well.
Gunnar

called the number for a virus called f.b.i warning,they fixed up my computer and the other three companies i called earlier were not able to fix the problem what the guys at this number fixed in 35 minutes .
really appreciate their help and got my computer working back again.

I found this number on a listing for Outlook Support.  The man I spoke to answered on the second ring (first sign it was not a real Outlook support line) and barely listened to my issue.  Then he asked me to open my browser to team viewer, and explained that he would have to take control of my screen in order to investigate my issue.  I told him I was not comfortable with that and I would prefer him to try to walk me through the problem.  He basically told me to have a good day and hung up.  Don't call 800-901-1275 !