The "Blaster" Internet worm claimed its biggest scalp in Europe on Thursday, reports Reuters, forcing the closure of 80 Finnish branches of Nordic bank Nordea.
According to the report, the worm infected servers in all of Nordea's 440 Finnish bank offices, forcing the one-day closure of about 80 branches.
The computer worm, also called MSBlaster or LoveSan, has quickly spread around the world, taking advantage of a security hole in popular Microsoft operating systems.
Reuters says Nordea has assigned a technical team to flush the infection out of its computers overnight.
A Nordea spokesman told Reuters that the worm had not affected its Internet banking system or corrupted any customer data.
The incident is hugely embarrassing for Nordea. Microsoft issued a patch to plug the security gaps exploited by the bug late last month.
In South Africa, Nedbank and First National Bank both admitted that they too had fallen victim to the infection. FNB moved to shut down its Internet banking system for a few hours while the outbreak was being investigated.