Hackers last week breached the systems of Myspace, the music-focused social networking site now owned by Time Inc., and have attempted to sell data on millions of users in an online forum, Time Inc. confirmed Monday.

The hackers responsible were offering to sell about 360 million Myspace user emails and passwords, Vice’s Motherboard tech site reported last Friday. Myspace — once a high-flying social networking site that had been acquired by News Corp. $580 million in 2005 — became part of Time Inc. after its acquisition of data marketing firm Viant in February.

Myspace said in a blog post that it believed the data breach was the work of Russian cyberhacker “Peace,” who was allegedly behind similar attacks on LinkedIn and Yahoo’s Tumblr. It said it has reported the hack to law enforcement officials and is cooperating with an investigation into the incident.

The info stolen from Myspace was limited to a portion of usernames, passwords and email addresses registered prior to June 11, 2013, when the site instituted stronger security measures, according to Time Inc. The company said the Myspace breach does not affect any of Time Inc.’s systems, subscriber information or other media properties and does not appear to include any financial data.

“We take the security and privacy of customer data and information extremely seriously — especially in an age when malicious hackers are increasingly sophisticated and breaches across all industries have become all too common,” Jeff Bairstow, Time Inc. exec VP and CFO, said in a statement. “Our information security and privacy teams are doing everything we can to support the Myspace team.”

Myspace said it has invalidated all user passwords for the affected accounts created prior to June 11, 2013, on the old Myspace platform, and that it is using automated tools to attempt to identify and block suspicious activity on user accounts.