A teenager in New Zealand has pleaded guilty to all charges he faced for his part in attacking the University of Pennsylvania's computer system and in a global adware scheme.

Owen Walker, the 18-year-old also known as 'Akill', pleaded guilty in the Thames District Court to accessing a computer system with the intention of dishonestly obtaining payment for the installation of adware, accessing a computer system without authorisation, and several other charges related to his role in the attacks.

The only victim loss that the police can quantify is the cost incurred by the University of Pennsylvania. The denial of service attack cost the university around $13,000 to mitigate, according to the police summary of facts.

Walker will be sentenced on 28 May, and a pre-sentencing report will be prepared between now and then. The pre-sentence report would cover home detention, community detention and community work, said Judge Arthur Tompkins.

Walker allegedly launched the DoS attack in collaboration with a second offender, Ryan Goldstein, a student at the university. Walker has admitted his association with Goldstein and to gaining access to the university's servers through him. Walker told police that he used the university's server to update his botnet, and that the DoS attack was unintended.

Goldstein pleaded guilty to the charges last month in a US court. If reparation is ordered, Walker's share would be around NZ$8,000 ($6,284.80) said the summary.

Walker received almost NZ$40,000 in total from adware companies for installing adware using his botnet, according to the police documents. He used the money to buy computer equipment and he also made investments in a business run by his parents. His mother and stepfather knew he was making money out of doing online work but they did not realise he was engaged in illegal activity, said the summary.

He was caught during an international investigation, Operation Bot Roast, during which his home was raided in November by New Zealand police and an FBI agent.