Attacks by Chinese hackers on US military computer infrastructure have reached the level of sustained cyber-warfare, and are likely to be government-backed, a senior US Navy official said last week.

The Naval Network Warfare Command official, who spoke on condition of anonymity, said that Chinese attacks far outnumber those from any other nation in frequency and sophistication, according to a report in Federal Computer Week.

"They will exploit anything and everything," the official said, according to the report. The attacks are so deliberate that "it's hard to believe it's not government-driven".

The report is the latest warning on the vulnerability of government systems to organised attacks from China. The most serious such attack against UK government targets occurred at the end of 2005, when messages exploiting an unpatched Windows WMF flaw were sent to around 70 recipients in parliament and other parts of the government. The attacks were later traced back to China, though government involvement was never confirmed.

Earlier this month, the Ministry of Defence admitted its systems have been penetrated at least nine times since 2002, with five of the successful attacks taking place last year.

The government did not say whether China was involved in those attacks, but China is the largest single source malicious software designed to covertly infiltrate systems - according to Sophos, 30 percent of such malware originates in China.

The MoD said it had taken steps to avert further attacks. "We focus on those attacks which have penetrated our gateways and have triggered incident-response actions designed to limit any damage and reduce risk of a recurrence," the ministry said in a statement.

Beginning in 2003, US defence agencies have been the target of a series of intrusions, code-named Titan Rain, that was traced to a team of researchers in Guangdong Province. Titan Rain was first reported publicly in 2005, and is still ongoing, according to Federal Computer Week.

In November 2006 another attack originating from China disabled the Naval War College's network, according to the report.

In a recent speech at the Air Warfare Symposium, Gen. James Cartwright, commander of the Strategic Command (Stratcom), said US strategy around internet warfare is hobbled by poor coordination among offensive, defensive and reconaissance efforts.