The Royal Navy website is still down after it was compromised by a hacker at the weekend.
The website has been replaced with a static image and a message which says, "Unfortunately the Royal Navy website is currently undergoing essential maintenance. Please visit again soon."
A Romanian hacker known as TinKode has claimed responsibility for the hack, and is reported to have posted usernames and website data on the internet.
TinKode has previously revealed security holes in NASA's website and published information about SQL injection vulnerabilities in sites belonging to the US Army.
But according to a Navy spokesman, no classified information was accessed and no malicious damage was caused by the attack.
The website has been suspended temporarily as a precaution. Security teams are investigating.
Security firm Sophos said the attack comes as a strong reminder to website owners of the importance of protecting their sites against attack.
"The MoD is lucky that on this occasion, those behind the hack have been motivated more by mischief than malice," said Graham Cluley, senior technology consultant at Sophos.
"All website owners should take note of this attack and the need to build secure websites that cannot be breached easily by hackers," he said.
According to Cluley, the Royal Navy could have found itself in a far more sinister situation if hackers had chosen to embed spyware onto the website and infected visitors' computers to steal classified information.
"Owners of other websites shouldn't be under the misapprehension that it couldn't also happen to them," he said.