I've just had a phone call from someone claiming to be the "Windows Help Desk" and saying that they're getting loads of error messages from my computer and that if I didn't do what they told me immediately, my computer would break down! The background noise sounded like they were calling from a large call centre and the accent was Asian.
Err.... I don't think so. We aren't stupid enough to sign up for a service like that for domestic computers (waste of money) and the people who run those services commercially don't make calls out of the blue on a Saturday. You have to register a problem first with the help-desk - they can't monitor you remotely (companies can, but that's because you log into the company network before you do anything else).
Also, I'm geek enough to know there is nothing wrong with either PC. If there was, I know a reputable business in Uxbridge that'll fix it for a flat fee.
However, someone who didn't have much technical knowledge might get caught out, follow their instructions and download the spy-bot as instructed or pay over the money for the service these scammers are selling.
For heavens sake, if you get a call like this, engage your common sense first and then hang up!