A PlaySpan breach by hackers has been shut down after the firm detected and terminated illegal access to the Marketplace.
However, user IDs, email addresses and encrypted passwords of Marketplace users were compromised.
"When PlaySpan detected the breach, we immediately shut down the hacker's access to our systems and took steps to protect our customers' PlaySpan accounts," the firm told Polygon.
"We then commenced a comprehensive forensic analysis and are working with law enforcement to investigate the crime. As a precaution, we have already locked all user accounts and closed the PlaySpan Marketplace site.
"If customers happen to use their PlaySpan Marketplace log-in information at other websites, including their e-mail provider, we are encouraging them to reset those passwords. In that regard, for those customers with PlaySpan Ultimate Pay accounts, we have implemented an automatic reset of all user passwords."
Games which use PlaySpan for microtranactions number over 1,000, with World of Tanks and Guild Wars 2 included in the list.
ArenaNet as said its "does not use PlaySpan for its micro-transaction services in Guild Wars or Guild Wars 2," as was reported by various outlets early today.