Last Pass is meanwhile working on stronger encryptions and has moved all services from the affected systems before shutting them down.

FORBES: Morning Tech Wrap: Sony, Last Pass, Electronic Arts

Others shut down their mail systems to keep clients and partners from being affected.

CNN: 'Melissa' mutates, becomes resistant to patch

"We have isolated all our electronic systems from outside access as an early precautionary measure that was taken following a sudden disruption which affected some sectors of our network, " the message reads.

BBC: Saudi Aramco oil giant recovers from virus attack