Australia's largest technology forums - Whirlpool and Overclockers - had security breaches at the weekend.
Founder of PC hardware forum Overclockers, James Rolfe, said he had become aware of the issue on Saturday.
"Unfortunately last night I became aware of a possible security issue on one of our servers and noticed some unusual activity," said Rolfe on his web site on Saturday.
Founder of broadband forum Whirlpool, Simon Wright, issued a similar statement on his web site.
"Unfortunately, Whirlpool has become aware of a security issue with the site that occurred over the weekend," said Wright.
Neither would make further comment to iTnews. Wright said any further statements Whirlpool chose to make would "be directly to our users".
But both left security measures on their sites that they said users could take to ensure they were secure.
"As a precaution you might want to change your forum password [and] change your password on any other services that use the same password," said Rolfe.
Wright left a similar warning.
"We recommend that you change your password, just in case."
Wright also said he had been in contact with Rolfe to investigate whether the incidents were related.
In August 2007, Whirlpool users were told to change their password after Wright said it was "possible that some forum data was able to be compromised".
This sparked concern that user's passwords were not stored using non-reversible encryption.
"Changing the database to store passwords with non-reversible encryption is a more difficult task and unfortunately isn't high on the priority list," said Wright at the time.