The scammers behind this scheme have now begun installing software that they buy with the victim's credit card - which might mean that police can now take action

The scam whereby people in Indian call centres ring up and insist that they are calling from "Microsoft Windows Support" and that they have been alerted - by Microsoft, or your ISP - that "your computer is running slowly because of viruses" - is still going on.

And they're still charging people for their fake "help", and people are still falling for it: I get a few emails a week confirming it (and that of course is only the people who realise they've been had). If you need confirmation, Microsoft's Answers system is stuffed with people asking about it

Until now, it has been a relatively harmless process: the call centre workers didn't leave anything (such as malware) on your computer, because that could involve the police internationally, and even in Kolkata (Calcutta as was), where the criminal gang that's behind this is based, the police might take notice. Nor have I seen any evidence that they steal details such as bank information. You got scammed for a couple of hundred pounds, but if you realised what had happened, you could get the payment reversed.

But something has changed: they seem to have started trying to install software. That takes the scam into new territory altogether, because it means that the scammers are now changing the setup of the computer, and while it's still fraud, it also now strays into fields such as the Computer Misuse Act.

The confirmation came in an email a few days ago from a man called Steven, based in Manchester, who was called from a company claiming to be "Windows Service Centre" based in East London (on the phone number 020 3318 3026).

"She advised that there were numerous error reports that had come through and that my computer was badly affected and running slow (which sounded true)," says Graham Steven. "I was taken through various screens, which induicated numerous warnings and alerts and it was suggested that as my computer care warranties had expired, I should purchase a new one."

Being wary, he called them back in case the phone number was fake. But of course the phone number worked: it's a VOIP line back to India.

The cost? £199 - which included the installation of Kaspersky Antivirus. With tax, it came to £240.

The scammers were careful, though: they used his card details to make the purchase. It was only afterwards that Steven realised his mistake: "I received an Invoice from "SWREG" [Digital River, a download service in the US] for the service and thought nothing of it, until I checked the possible frauds page that you have. I phoned my credit card company, who confirmed that the transaction had gone through, so I immediately cancelled my card. A friend came round and uninstalled all of the Kaspersky and other applications. I do not know for sure that this is a scam, but strongly suspect that I have been conned."

Unfortunately it is a scam, and he has been conned. But he may be able to get the money back.

If you, or someone you know, falls victim to this scam, then do three things:

1) contact your card issuer and get the transaction reversed

2) report what happened to Action Fraud, the UK's national fraud reporting centre. It has its own page on Microsoft-related scams, as does Microsoft itself.

3) contact the police so you can get a crime number.

If you do a search on the phone number given, you find that it appears on a number of sites - including one calling itself YTech Solutions (ytechltd.com), which looks like another standard template for the scam; the sites are set up by the dozen, and as soon as police get one taken down, six more are ready to spring up - with similar misspellings, "privacy policies" and so on. YTechltd hides its ownership details behind a domain proxy - hardly what you'd expect from a reputable company.

People are still getting these calls - often multiple times. The clue though that there is a single gang behind all this - rather than multiple people trying their luck - comes from the fact that I've never come across anyone who has been phoned twice once they've taken out this "support". That suggests that they are keeping some sort of database - but the other question is, where do they get their database of people to call?

Updated: Corrected name - victim's name is Steven, not Graham. Added third thing to do - contact police. Misspellings corrected.