Copyright protection software that was embedded in thousands of Sony BMG music CDs is causing computers to slow down, and making them vulnerable to hackers.

About 120,000 of the CDs were sold in Canada. Sony BMG did not immediately disclose which artists' albums were affected, other than to say 37 titles are involved.

The software, called XPC, is intended to stop piracy. When customers play or try to copy the music using their computers, spyware software becomes installed on the hard drive.

Once installed, the spyware runs continually, slowing down operating systems and making computers vulnerable.

"It would be kind of like leaving your back door unlocked," Jason Gibson, a computer support worker, told CTV. "Someone could potentially come right in. It doesn't mean it's going to cause problems right away -- but it could do damage."

Sony BMG has recalled the discs. About 4.7 million had been made, and 2.1 million sold including the 120,000 in Canada.

Sony BMG spokesman John McKay said the company will list for Canadians all the affected titles by Monday on its website, cp.sonybmg.com/xcp.

Sony BMG stressed that the majority of its catalogue sold in Canada uses an "alternative copy protection technology" and is safe to use.

"We are dedicated to making this situation right,'' McKay said.

The CDs only cause problems when used in a computer, not in a traditional CD player.

All Sony BMG CDs which are embedded with the XPC software carry a copyright protection trademark on the back of the CD jewel case.