Owen Thor Walker used the botnet to skim an estimated £10m from the bank accounts of internet users as part of an online gang.
The 18 year-old was caught in November during the FBI's Operation Botroast II, which is trying to track down virus writers and botnet owners.
Walker wrote the code that allowed others to bypass anti-malware filters and install a Trojan that specifically harvested bank account details.
It is unclear whether he significantly profited from accessing the bank accounts, but he did sell his code to others.
Using the online name 'Akill', Walker wrote the code while still a minor. But after pleading guilty to six charges of accessing a computer for dishonest purposes, interfering with computer systems, possession of software for committing crime and accessing computer systems without authorisation, he could face up to seven years in prison.
However, Judge Arthur Tompkins said in court that, because of Walker's youth and his affliction with Asperger's Syndrome which can result in deficiencies in social skills, he would not be considering a custodial sentence.
Graham Cluley, senior technology consultant at Sophos, said: "In some ways he is a young guy so why ruin his life with a jail sentence that would cast a shadow over his whole life.
"If he didn't make a lot of money doing this then he probably won't do this again. At the same time there are a lot of young people out there with the skills who may be tempted to give it a try."
NZ teenager admits to million-PC botnet scam
By Iain Thomson on Apr 2, 2008 7:42AM