Tesco Bank hackers probe led by National Crime Agency cyber sleuths

UK's National Crime Agency (NCA) is leading a criminal probe into the recent cyber attack on Tesco Bank, which saw about 20,000 accounts raided by tech-savvy hackers.

It said the National Cyber Security Centre (NCSC) was working with Tesco Bank and others to provide direct assistance to the company, at its request.

"Given the investigation thus far and the evidence at hand, the NCSC is unaware of any wider threat to the UK banking sector connected with this incident," the NCA said in a statement.

NCSC was set up up about a year ago with the task of handling cyber incidents in UK.

Meantime, about 20,000 Tesco Bank customers had money filched from their accounts by hackers over the weekend.

Some account holders had up to £600 siphoned off. Tesco Bank initially claimed less than 10,000 customers were affected.

On Monday, it said about 40,000 customer current accounts had been "subject to online criminal activity" with half that number seeing money being withdrawn fraudulently.

The bank took the precautionary measure on Monday of temporarily stopping online transactions from current accounts. It has 136,000 accounts.

It was not immediately clear how much dosh the hackers had taken, but preliminary back-of-envelope workings based on the above figures suggested up to £12m. Tesco Bank would need to confirm the precise amount.

Apart from saying the fraud was committed via "online criminal activity", the bank has not yet given any details of how exactly the fraud was committed.

Professor Alan Woodward, a security consultant who has worked with Europol, told the BBC he thought it might have been the biggest ever cyber attack on a UK bank.

"I've not heard of an attack of this nature and scale on a UK bank where it appears that the bank's central system is the target," he said.