The 24-year-old man was arrested on 23 July, but Scotland Yard and the FBI, who conducted a joint operation, delayed the announcement until yesterday due to ongoing investigations.
A spokesman from the Metropolitan Police said that officers from the Computer Crime Unit obtained a warrant to search the man's south London address before making the arrest. He has been bailed to return to the police station on 24 September.
The man, who cannot be named for legal reasons, was arrested for allegedly writing and spreading the W32.Leaveworm, which attacked Windows-based computer systems earlier this year. The worm appeared to be a Microsoft e-mail about security. It worked by leaving a back door into infected systems, which permitted intruder access while connected to the internet, without user knowledge.
"We did not come across the worm," said Paul Rogers, network security analyst at MIS Corporate Defence Solutions. "It was given a low-threat assessment risk. Cynical people might say it was an easy target for the law enforcement agencies, so [that] it looks like they are doing some work."
The arrest follows a spate of activity by the FBI to bring suspected hackers to book, including the arrest of Russian cryptographer Dmitri Sklyarov, charged with trafficking in a device allowing the decryption of Adobe Systems software for electronic books. Sklyarov maintains he was involved in legitimate security research.