Popular Irish internet forum Boards.ie has reported an attack on its user database which could affect thousands of users.
In a statement on its website, it confirmed that 'an unauthorised source' from outside Ireland accessed its database server this morning.
'Part of the database which includes our members’ usernames, email addresses and obfuscated passwords was accessed.
Boards.ie has asked all members who use the same username/email and password on other sites to change passwords as a precaution.
'Like all large sites we are regularly the target for disruption and take continual actions to proactively protect your data,' the statement said.
'This particular attack was completely unprecedented despite our rigorous security measures and while we have no idea if this data will be used for any malicious reasons, we felt it vital to tell you this immediately.'
Boards.ie says it is changing all user passwords and has notified gardaí.
The Data Protection Commissioner Billy Hawkes has said today's attack on boards.ie should be taken as a warning to internet users to create different passwords for different websites.
Mr Hawkes said his office would be investigating the security breach but he praised the company for pulling the website immediately and alerting its members.