The St George Internet banking site crashed late this afternoon without warning creating havoc at the bank which said it was unable to confirm when the service would be back in operation.
A St George media spokeswoman confirmed the service has shut down but said staff were still unclear about why it occured and were busily trying to work out what to do.
However, a St George customer and IT manager for a large organisation who didn't wish to be named, said it looked like a Denial of Service Attack (Dos).
"The site has been congested most of the day prior to it crashing between 4.30pm and 5pm this afternoon," he said.
The St George spokeswoman said more details about the shutdown will be available once the cause of the problem has been identified.