The FBI on Friday arrested Jeffrey Lee Parson, 18, from his suburban Minnesota home on one count of intentionally causing or attempting to cause damage to a computer.
He admitted to creating a variant of the worm, according to a complaint filed in the Western District of Washington state, where Microsoft is based in the Seattle suburb of Redmond.
Parson said he modified Blaster and created a variant known by different names, including "W32/Lovesan.worm.b". He also admitted that he renamed the original code dubbed MSBlast.exe" "teekids.exe," after his online alias, the complaint said.
FBI agents interviewed Parson when they searched his home on 19 August and seized seven computers.
Blaster and its variants are self-replicating internet worms that gained access into Windows machines through a security hole, allowing them to launch concerted data attacks via the internet on a Microsoft technical service Web site.
At least 7000 "drone" computers tried to attack the Microsoft Web site, the complaint said.
Microsoft has been able to thwart the attacks by disconnecting the Web address from the internet.
Versions of Blaster cause infected computers to close down and restart frequently.
Blaster is believed to have infected hundreds of thousands of computers worldwide since it was released on 11 August.