Santander says no customer data is at risk after the failure of one of its online banking systems.
Internet forums, including the MoneySavingExpert.com forum, have been full of rumours this morning that the Alliance Leicester (A&L) log-in page had been hacked.
However, following hurried investigations this morning the Spanish giant insists no customer data has been stolen but admits one of its systems experienced a "failure".
A&L merged with Santander last year though anyone who opened an account with the former must still log-in using the A&L site.
The technical team at MoneySavingExpert briefly looked at the A&L code – the complex formula of letters and numbers that make up an internet page – and found what appeared to be worrying problems.
It initially seemed a third party had the ability to steal log-in details, though Santander says that third party is known to it and the glitch made it wrongly appear to be a hack.
A Santander spokesman says: "Santander's internet banking systems utilise a number of third parties and one of these appears to have had a technical failure.
"It is being corrected by a third party and this is not an online banking security issue."
The bank had added the following warning to its Santander online banking log-in page, but not its A&L page, as a precaution: "UK banks are currently being targeted by fraudsters attempting to capture security information.
"Customers have reported seeing a pop-up window requesting online and telephone banking details.
"DO NOT enter security information into any pop up window. If you suspect that your security details may have been compromised call us immediately on 0845 6004388."
Santander has been beset by customer service problems for the past year.
It has consistently come bottom of our banking customer service polls, while in December it sent 22,000 statements to the wrong addresses.