The US Department of Homeland Security (DHS) is "unlikely" to protect the country from the most dangerous cybersecurity threats, according to a report from the US Senate.

Authored by senator Tom Coburn, who retired at the start of the year, the report claims that despite spending more than $700m (£460m) a year in cybersecurity programmes the DHS was "struggling to execute its responsibilities" in the field.

"Although the Department’s law enforcement agencies are involved in arresting criminals who violate our laws and attack our nation’s information systems, a majority of the Department’s resources for cybersecurity are spent on a strategy to help the government and the private sector defend its networks," he said.

"The nature of cybersecurity threats — and the ability of adversaries to continuously develop new tools to defeat network defences — means that DHS’s strategy for cybersecurity, which focuses primarily on vulnerability mitigation, will not protect the nation from the most sophisticated attacks and cybersecurity threats."

The report argued that firewalls and vulnerability mitigation are of limited use due to hackers ability to circumvent them, citing Stephen Chabinsky, a former FBI official, who called for a greater focus on deterrence in a committee hearing last March.

William Noonan, deputy special agent in charge with the U.S. Secret Service, also said to the committee: "Current research on the cost of cybercrime indicates that preventing cybercrime through investigations, arrests, and deterrence is an effective means to reduce the aggregate economic cost of cybercrime."

It was also revealed that an audit by the inspector general, a civil service watchdog, had shown that the department’s own offices did not fully comply with federal rules for agency cybersecurity.