ABBA's Bjorn Ulvaeus has hit out at illegal downloaders and supporters of controversial website The Pirate Bay.

Ulvaeus' comments come during the trial of the four founders of the torrent website, which is currently underway in Sweden.

Writing on Swedish website Newsmill, Ulvaeus lambasted internet users who steal online music, and think it's OK to do so.

"It is easier and cheaper to steal than to download legally," he wrote, before describing torrent services as offering people "the 'freedom' to be lazy and mean".

Refuting suggestions that sites like The Pirate Bay symbolise a 'Robin Hood' scenario towards music fans, the ABBA star said he can't understand why people don't simply pay for online music.

"Is it so fucking hard to understand?" Ulvaeus asked. "Is it really so damn difficult to pay your way?"

Ulvaeus' attack comes after prosecutors in The Pirate Bay case had to drop 50 per cent of the charges against the founders because of shortcomings in evidence.