Hackers broke into databases of the popular online role-playing game "Second Life" and accessed 650,000 player names, addresses, and passwords, prompting the developer to order all players to change their log-ins.

The breach, which was discovered Wednesday, Sept. 6 by game maker Linden Lab and disclosed Friday, Sept. 8 in an alert on the "Second Life site", was carried out via a zero-day exploit against unnamed software running on Linden Lab's servers. Players' credit card information, which was stored in another database, was encrypted and not compromised, the company assured users.

"Detailed investigations over the last two days confirmed that some of the unencrypted customer information stored in the database was compromised, potentially including Second Life account names, real life names and contact information, along with encrypted account passwords and encrypted payment information," read an associated alert on the San Francisco company's blog.

"We're taking a very conservative approach and assuming passwords were compromised and therefore we're requiring users to change their Second Life passwords immediately," said Cory Ondrejka, the chief technology officer at Linden Lab, in a statement. "We believe it's the safest course of action."

The company invalidated all "Second Life" passwords Friday, forcing users to create new passwords to reach the game. On Saturday, it offered up other password-reset options; Monday it posted toll-free numbers for users in the U.K. and Australia.

Attacks against massive multiplayer online games (MMOG) have come under attack as the value of the virtual goods -- including characters cultivated by players -- has climbed and become easier to translate into real-world currency. In April, for example, Blizzard Entertainment of "World of Warcraft" fame purged over 15,000 users accused of using cheats to "farm" in-game goods, which they then sell to other players for real money.