WPP has been thrown into chaos by a cyberattack that, according to an internal Y&R memo, is causing the company to suspend work on desktops and PCs.

The attack appeared to strike agencies across WPP, but it wasn't clear whether all agencies were affected, though tweets indicate Ogilvy has been affected. "Ogilvy currently under a large cyber attack. Just been told to shut down all Macs and PC's, ransom demands the works. Fun times," tweeted @swhiteley.

As of 11:30 a.m. ET, WPP's website displayed a message that it was currently unavailable "due to important routine maintenance." The company tweeted that "IT systems in several WPP companies have been affected by a suspected cyber attack. We are taking appropriate measures & will update asap."

A later memo from Y&R said, "As a precaution, WPP is mandating that everyone immediately shut down all computers, both Macs and PCs. This applies to you whether you are in the office or elsewhere. Working on an office computer remotely is not an option. Please leave your computers turned off until you hear from us again. "

A company spokesman told Ad Age to monitor its Twitter page for further information.

According to Reuters, WPP is one of many places hit by a ransomware attack, including Ukranian and Russian Banks, Maersk and potentially others. Mondelez released a statement saying its "international network is experiencing a global IT outage. Our global special situations management team is in place, and they are working to resolve the situation as quickly as possible. We will update as we have more information."

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