British bank HSBC said it had successfully repelled a cyber attack on Friday although online access to banking services was not possible.
"HSBC UK Internet banking was attacked this morning. We successfully defended our systems," HSBC UK tweeted. "We are working hard to restore services, and normal service is now being resumed," it said.
A spokesman specified that the attack was a "denial of service attack", which slows down or disables a network by flooding it with communication requests.
Users attempting to access the bank online were met with a message saying: "Sorry, there appears to be a system problem. Please try again later."
HSBC, Europe's biggest bank, suffered a series of online banking glitches earlier this month but said this was a technical problem not a cyber attack.