With its website back up and running, the Recording Industry Association of America (RIAA) has stepped up its legal campaign against suspected file swappers.

The music industry body has filed another 532 lawsuits across the US, of which 89 are believed to be against students at 21 US universities, who it accuses of using "university networks to illegally distribute copyrighted sound recordings".

The RIAA has had to file what are known as 'John Doe' lawsuits, as the identity of each peer-to-peer (P2P) user is known only by the IP address they use.

With many of its 1,063 John Doe lawsuits filed since January, courts have granted the RIAA's request for preliminary subpoenas against ISPs to hand over individuals' details.

The association expects the courts to grant the same permission for 531 John Doe suits it filed in February.

Before it takes any further legal action, the RIAA said it would send letters to individuals offering to settle out of court.

Some 408 P2P users prosecuted by the RIAA since last September have settled out of court, paying fines of around $3,000 per person.

RIAA president Cary Sherman said in a statement: "Lawsuits are an important part of the larger strategy to educate file sharers about the law, protect the rights of copyright owners and encourage music fans to turn to these legitimate services.

"It's important for everyone to understand that no-one is immune from the consequences of illegally 'sharing' music files on P2P networks."