Once they won access to the computers, the pair downloaded police and social security files.
Mr Warg will be sentenced on 31 October and could face six years in jail.
His accomplice walked free from the court on 30 October as he had served 17 months in pre-trial detention.
The initial hack attack took place in February 2012 and gave the pair access to the sensitive information for about six months.
Defence lawyers said although the hack attacks were carried out using a computer owned by Mr Warg, he was not the person that used it to steal the files. Instead, they said, an unnamed hacker took over this machine and used it to carry out the attacks. Mr Warg has declined to name this other hacker.
After considering evidence, the judge and jury in the case said it was "unlikely" that other people were responsible.
The court's decision is the third to go against Mr Warg in the last five years.
He was deported from Cambodia in September 2013 to Sweden where he served a jail term for copyright theft because of his involvement with the Pirate Bay file-sharing site.
In a separate trial in 2013, Mr Warg was sentenced to two years in a Swedish jail for hacking into a bank's computers. This sentence was reduced to one year on appeal.
In that trial, Mr Warg and accomplice were found guilty of breaking into the computer systems of computer services firm Logica, which was doing work for Sweden's tax office and a bank. On that occasion his accomplice was put on probation.
In late November 2013 he was deported to Denmark to face charges in the CSC hacking cases.