The man on trial for writing the Sasser computer worm that wreaked havoc in big businesses and homes across the world last year has confessed to all the charges against him, a German court said on Tuesday.

Katharina Kruetzfeldt, judge at the court in the western town of Verden, said Sven Jaschan, 19, admitted to data manipulation, computer sabotage and interfering with public corporations in one of the biggest Internet attacks of its kind.

After emerging around May last year, versions of the Sasser worm went on to knock out an estimated 1 million computer systems among home users and companies by spreading on the ubiquitous Microsoft Windows operating system.

Sasser victims ranged from the British Coastguard to the European Commission, Goldman Sachs and Australia's Westpac Bank. Some security firms called it the most destructive worm ever.

State prosecutor Silke Streichsbier said she was "highly satisfied" with progress made at the trial, which is closed to the public as Jaschan was a minor when some of the offences took place. A verdict is expected Thursday.

Jaschan, who had previously confessed to having created the worm to police, could face a maximum sentence of five years in prison as well as having to pay compensation to his victims.

Prosecutors said damages amounting to some 130,000 euros ($154,600) had so far been reported by victims of the worm, but the figure could spiral into millions if everyone affected worldwide were to report financial losses caused by the worm.

How the 19-year-old was expected to pay such compensation was not immediately clear.

Jaschan, described by authorities as a "computer freak," was identified as the author after Microsoft offered a reward of $250,000 for information leading to his arrest.

It is believed he began creating programs, including the Netsky virus, to seek out and destroy other viruses.