Our hapless reader noticed the dubious entry on his credit card bill and spotted it immediately as a fraud. So he quickly rang T-Mobile to complain.
Reputedly the agent in T-Mobile's help centre sounded very familiar with the situation and suggested that the company was currently experiencing problems with fraudulent top ups.
His advice was to cut up the credit card immediately and order a replacement. Presumably the hacker had been able to scam the three digit verification code on the back of the card.
One of the problems with pre-paid is that the networks don't actually know who the real owner of the handset is. It seems that T-Mobile's online sign up system for topping up doesn't even require a postal address.
So the INQ speculates that the system isn't checking credit card numbers against a postal address when adding top ups.
The INQ is waiting for T-Mobile to get back to us about this. Meanwhile, check your credit card bill. µ