DavidR
4
Neither Dell or iYogi would be able to identify you by your IP address (which changes) and also have your telephone, it is nothing other than a speculative telephone scam.
Just do a google search for Microsoft Telephone Scam and there is no scam by microsoft, just the scamming pond life using common names. Interestingly this one has just reared its head and this time it is/was an MS partner responsible for the scam and they have been binned.
http://www.google.co.uk/search?q=Microsoft+Telephone+Scam
This however was the one which was doing the rounds some time ago, http://www.guardian.co.uk/world/2010/jul/18/phone-scam-india-call-centres. So looks like the same telephone scam but just a different script and company names used.