Those who paid on-line for Which? TaxCalc software were approached on Friday by the CA. The TaxCalc.com site, which was designed to help self-employed people to complete self-assessment tax forms, has been shut down until the fault can be fully traced.
Kim Lavely, deputy director of the Consumers' Association, said in a statement on the Which? Online web site:
"This is a serious flaw in the security of the TaxCalc site and we are very concerned about it. As soon as we were alerted to the flaw, we removed all personal and financial details from the TaxCalc site. We have already commissioned an independent security expert to conduct a thorough audit of the security of this site. The TaxCalc site will remain shut until this problem has been resolved. We are contacting all customers who have bought TaxCalc from this website, informing them that their personal and financial details have been compromised. We will be advising them to contact their credit card issuers to cancel their cards."
The group, which campaigns for better security in on-line transactions, has blamed a fault in its system for the accident. It stressed that users of other Which? Online services were not affected.