A gaming "virtual world" has been knocked offline for the second time in a month by malware distributed by players within the game. Second Life, an innovative online game with more than 80,000 users, took its entire system down for more than five hours Thursday after an instant messaging bot overwhelmed the game grid with a huge volume of messages. A similar incident on Oct. 23 also caused a lengthy system outage when a user program automatically generated more than 5 billion spheres inside the game.

A user-designed multiplayer world, Second Life encourages programmers and graphic artists to create virtual goods and services to sell, and allows players to convert game currency into real-world cash via an online exchange.

That approach has empowered users to create virtual businesses selling Second Life real estate and digital clothing, but also made it easy for in-game "griefers" to create malware, a long-standing problem which has escalated in recent weeks to affect the entire game. "Few other environments allow their residents the ability to create malicious software capable of disrupting service," notes blogger Tony Walsh of Clickable Culture. "Currently, deploying such software is not allowed - but it is both possible and easy."

In Second Life's cash economy, downtime is money - at least according to one user, who claimed Thursday's outage derailed a business transaction valued at 37,000 in-game "Linden dollars" - an amount worth about $140 on external trading portals and more on Second Life's in-game exchange.

The outages follow a large increase in compromised accounts on World of Warcraft, the largest massively multiplayer online role-playing game (MMORPG) with more than 4.5 million users. Many of the account thefts were related to a keylogger trojan injected into a banner ad system on a popular World of Warcraft fan site. The large volume of account thefts forced game operator Blizzard Entertainment to add extra support staff shifts during October.