Computer details of current and former defence staff, including a former Royal Navy head, were posted on the internet after a hacker broke into a military website and shut it down.

The Royal Navy website was taken offline after being "compromised" by the hacker, codenamed TinKode, who has a history of breaching government databases including Nasa, the US Space Agency and the Pentagon.

The Ministry of Defence stressed yesterday that no "malicious damage" had been inflicted on the Royal Navy site, which did not contain any classified information. However, the site has been down for three days and TinKode, who is Romanian, posted so-called "hash values" for Ministry passwords he claimed to have obtained from his illegal entry. With hash values, hackers can crack passwords a lot more easily. One of the named accounts was for former First Sea Lord Admiral Sir Jonathon Band.

In the wake of the disclosure, other hackers piled in with additional material including five passwords for other members of staff. The MoD insisted that the information posted would not allow anyone access to secrets.

The electronic break-in took place on Friday night. Visitors to the website yesterday morning were greeted with the message "Unfortunately the Royal Navy website is currently undergoing essential maintenance. Please visit again shortly." A message posted by TinKode on the social networking site Twitter read: "Minister (sic) of Defence United Kingdom – HACKED". According to members of the hacking community, TinKode used to be a member of Hackers Blog, a collective of cyber activists who ran a campaign of breaking into websites to highlight security flaws.

Members of the group were known as "white hats" who did not harm the websites. But TinKode is said to have since become a "grey hat" – someone who deliberately publishes sensitive information online.

TinKode is believed to have used a "SQL injection attack" to target the Navy website, a common method which exploits vulnerabilities in databases used by websites. Once entry has been gained, the hacker can look at and download sensitive data as well as upload malicious software.

Rik Ferguson, a cyber security analyst at the company Trend Micro, said: "It's always embarrassing when something public is successfully hacked and should serve as a warning to anyone who has a presence online to take all the necessary steps to secure their websites." The MoD said: "There has been no malicious damage, but as a precaution the website has been temporarily suspended. Security teams are investigating."

Officials said the site had the level of security needed to prevent "things like silly pictures being put in". TinKode's actions, said one official, added nothing to the debate on cyber security.

Belfast Telegraph