Hello I'm from Microsoft ...

This is a phone call that almost everybody has had although I still get the occasional client who rings up in a panic because of one of these calls. The calls are a scam. They tell the potential scamee that they can tell that they are having problems with their computer. Now this must have a pretty good hit rate as almost every household has at least one computer and probably most of these have one or more problems.
To further enforce the idea that they know what is happening they get the scamee to do bring up a log that shows hundreds of events on the computer.
Well this is the event log and all computers have thousands of entries so again another safe bet. What they do  then is get the client to let them remote onto their computer. The scammers then bang around for awhile on the computer at the end of which they try and convince the sucker  client to buy some unneeded software at 500 percent markups.
The best response to these guys is to just hang-up the phone. If you have let them onto your computer and you are worried then call your local computer support guy to give your computer a once over.