The Ministry of Defence is battling a wave of copycat attacks after a hacker took down the Royal Navy's public website this week.
Simon Kershaw, head of defence security and assurance services, said IT staff have been monitoring many more attempts to penetrate military sites than usual since the hack, which emerged on Monday.
The site remains offline today, replaced by a screenshot and a message saying it is undergoing essential maintenance.
Kershaw, speaking at a cyber security conference in London yesterday, said he had spent much of the week persuading Royal Navy chiefs not to bring the site back online until vulnerabilities are patched and security checks completed.
A Romanian hacker calling himself "TinKode" claimed responsibility for the hack, which received widespread media coverage.
Kershaw confirmed he used a "simple" SQL injection to gain access to the website server. The MoD said that no confidential data had been accessed or stolen.
Nevertheless, the hack was embarrassing for the government, coming less than three weeks after it announced £650m in new funding for cyber security. The four-year budget is meant to strengthen its networks against threats from more serious adversaries than a solo "grey hat", including foreign intelligence agencies and organised criminals. ®