Wells Fargo is the latest bank to succumb to tech gremlins, leaving customers locked out of their mobile and online banking accounts on Thursday.
The US giant took to Twitter at about 9am EST to confirm an "issue", promising to research. Nearly four hours later, the problem had been identified as a "system issue due to a power shutdown at one of our facilities, initiated after smoke was detected following routine maintenance".
The problem appears to have occurred at a Minnesota data centre, when a "fire suppression" system was set off by accident. Fire Chief Tim Boehlke of Lake Johanna Fire Department told CNBC that there was no fire.
By 3.30pm EST, the bank had still not confirmed whether the problem had been fixed and was on the receiving end of hundreds of irate tweets.