I have recently been reading on another forum about someone(s) hacking into the Tesco Reward Server and people have found that their accounts are empty; upon checking with Tesco their rewards have been converted to Air Miles. Tesco was slow to react, thinking it was a one off but as the word spread they are now taking it seriously.
If you have a reward account with Tesco, you are being urged to check it and if it has been emptied to get in touch with their Reward Centre Helpline to report it. This has also been posted on Martin Lewis' website.
Hope you haven't been robbed.