Police in Lower Saxony, Germany, arrested five young men on Tuesday in connection with the Sasser Internet worm but all have been released without charge, a police spokesman said on Thursday.
One of the young men arrested confessed to having been involved with distributing the NetSky worm, released earlier this year, but he has not been charged in relation to that case, spokesman Frank Federau said.
An 18-year-old German man, identified in news reports as Sven Jaschan, was arrested in Lower Saxony on 7 May and confessed to having created both the Sasser worm, which first appeared on 1 May, and NetSky. He said he did so in an attempt to fight other worms, the Mydoom and Bagle worms, German authorities said at the time.
His arrest followed a tip-off to Microsoft from people hoping to gain a reward for the information. Microsoft said that it would consider a reward of up to $250,000 if their information led to the arrest and conviction of the Sasser creators.
Since Jaschen's arrest and confession, other variants of the Sasser worm have appeared, suggesting that other people are involved.
Sasser exploits a hole in a component of Windows called the local security authority subsystem service, or LSASS. Microsoft released a software patch, MS04-011, on 13 April that plugs the LSASS hole, but many companies and home users had not installed it in time to prevent the Sasser worm affecting their systems.