The producers of popular online world Second Life were forced to lock users out of the simulation on Sunday after attackers slowed the system to a crawl.

According to a post on the official Second Life blog on Sunday, the attackers used a method known as a "grey goo" attack — inserting self-replicating objects whose rate of growth forces the system's computers to spend most of their time creating the items.

The attack leaves little to no processing power to handle normal operations, such as drawing people's characters and updating their movements through the three-dimensional world.

"An attack of self-replicators is causing heavy load on the database, which is in turn slowing down in-world activity. We have isolated the grey goo and are currently cleaning up the grid," read a blog post by Robin Linden — the online name of Robin Harper, the senior vice-president of community for Linden Research, Inc., which created Second Life.

"Log-ins will be closed to all except Linden staff while we finish cleaning up the aftermath of the grey goo attack," read another notice about half an hour later, at 3:07 p.m. PST.

By 3:18 p.m. PST, Linden posted a notice that the problem had been fixed and users could log in once again.

Users lament problems

Sunday's attack — which was manifested as gold rings like those in Sega's popular Sonic the Hedgehog series of video games — appeared to add a new dimension to grey goo attacks, which have recently become an increasing problem in Second Life.

"Word on the groups is that the rings are physical, adding another dimension of sim lag," a user going by the online handle Feynt Mistral wrote in a comment on the blog post, a fact confirmed a user posting as RobbieRaccoon Olmstead.

He wondered whether a fix Linden Lab had previously implemented to prevent grey goo attacks had proved insufficient to defend against the new form of attack.

"Linden Lab, it's time to seriously think about these problems as real problems that are going to affect all of us and your bottom line," wrote a user dubbed Sunspot, wondering whether the company's pursuit of rapid growth was a wise course of action.

"It sure is a good thing that getting one million sign-ups was so important when the existing structure can't hand 15,000 users logged in," Sunspot wrote.

The company warned users last week that a program called CopyBot was making it possible for people to copy any object in the online world — a potentially grave threat to the simulation's virtual economy, in which digital entrepreneur users make and sell in-world items such as cars and clothes.
Earnings derived from Second Life transactions in so-called Linden dollars can be exchanged for real-world currency.

Second Life is frequented by hundreds of thousands of people and is one of the world's fastest growing virtual economies.

A company spokesman could not be immediately reached for comment.