A mystery viral infection forced the FBI and US Marshals Service to pull the plug on parts of their respective computer networks on Thursday, AP reports.

A spokesperson for the US Marshals Service explained that it had disconnected some of its computers from the wider Justice Department systems, as a precaution against spreading the as yet unidentified malware further. Access to internal email and the internet is being restricted at both the FBI and Marshals service while techies try to identify the precise cause of the problem.

Both government agencies stress that only unclassified systems are affected by the issue and that operations are proceeding as normal, despite the computer hiccup. Each is downplaying possible fears that the breach might lead to the compromise of sensitive data. ®

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