A MAN stole $42,000 after hacking into eBay and Commonwealth Bank accounts last year, with eBay now set to trial individual security keys to protect members.

The Commonwealth Bank has had online security keys, or "key fobs", since January. The devices are small electronic gadgets that generate a number that must be typed into accounts to verify access and transactions.

Dov Tenenboim, 21, of North Bondi, used his home computer to hack into at least 90 different eBay seller accounts last year, according to police.

After hacking into the eBay accounts of Wendy Runge and Kathy Gill, he sold $13,482 worth of nonexistent Apple iPod music players. After each sale he would direct his victims to pay for the goods by transferring money into the bank accounts of his accomplices.

By using other sellers' accounts, Tenenboim was able to take advantage of their good reputation to fool buyers into thinking the deal would be good. He also hacked into the Commonwealth Bank phone and internet banking account of Hugh Devlin last August.

Tenenboim, who was unemployed at the time of the crimes, pleaded guilty in the Downing Centre Local Court on Thursday to two counts of making a false statement to obtain money, two counts of obtaining money by deception and four counts of committing an unauthorised computer function.

Tenenboim faces a maximum of 11 years in jail and fines of $9900 for the eight guilty pleas. An additional 28 charges will be taken into account when he is sentenced on May 1.

Tenenboim's main hacking tool was perseverance - and victims with simple passwords.

"The evidence shows that Dov Tenenboim [was] gaining access to eBay accounts, mainly through guessing the passwords of the users, for example by trying the eBay seller name as the password," police said. He also hacked into sellers' email accounts and reset their eBay passwords.

The investigation was led by Detective Senior Constable Russell Ng from the NSW Police Computer Crime Investigation Unit.

An eBay spokesman, Daniel Feiler, said the company had compensated many of the buyers who lost money.

"What the case highlights is the importance that people need to place in choosing a sensible password," he said.