Computer hackers suspected of working from Russia successfully penetrated Pentagon computer systems in one of the most severe cyber attacks on US military networks. The electronic attack was so serious that Adm Michael Mullen, the chairman of the joint chiefs of staff, briefed President George W Bush and Robert Gates, the defence secretary. Defence officials told the Los Angeles Times that the attack struck computers within the US Central Command, which oversees Iraq and Afghanistan, and involved malicious software – known as “malware” – that permeates a network. “This one was significant, this one got our attention,” said an official, speaking anonymously.

Officials did not disclose the extent of the damage and would not elaborate on the reasons for believing the assault originated in Russia. The Pentagon and other US government departments face repeated cyber attacks, especially from Russia and China, either from individuals or indirectly from those countries’ governments. Within the past 18 months Russia has been accused of orchestrating major electronic attacks on neighbours Estonia and Georgia.