TSB is warning customers not to reveal their security details, as thousands of users face a second week of not being able to access their accounts.
The bank tweeted a warning to customers not to give out their PIN or password, prompting concern that fraudsters are taking advantage of problems at the bank.
TSB’s computer systems went into meltdown more than a week ago as the bank attempted to move millions of customer records over to a new system.
Thousands of customers have been unable to access their bank accounts and some have reported being given access to other people’s savings.
Chief executive Paul Pester is due to face questions from MPs on Wednesday. The bank boss last week said he was “working around the clock” to fix the problems, even asking tech giant IBM to find a solution.
The bank said this weekend that internet and business banking were operating again, but some customers are still reporting problems.
Now customers are concerned that fraudsters may be looking to take advantage of the situation after the bank issued a warning on social media to its 48,500 followers, urging people to keep their personal details safe.
The bank tweeted: “Customers have made us aware that they are receiving emails and tweets claiming to be from TSB. Please remember we would never ask you for your security details such as PIN or full password and we would only contact you via social media from our Official Twitter or Official Facebook page.”
Customers took the opportunity to respond to the bank. One user, Jon Skinner, said: “Even if I gave them all my details, it’s not like they can log in. Ten days later and your accounts are still not working and online banking is still down. Ridiculous.”
Mr Skinner added: “To be fair, this is opportunist crooks taking advantage and TSB are trying to alert people. But TSB still created the opportunity in the first place.”
A TSB spokesperson said: “We are sorry for the difficulty or distress you [customers] may have experienced and we are working round the clock to put things right.”
The bank says debit cards are working normally and customers can check their bank balance at an ATM and that direct debits and standing orders are working normally, with payments made into accounts working well for “most customers”.