ACS:Law, the firm of solicitors being investigated by authorities over thousands of threatening letters to alleged unlawful filesharers, was attacked by net activists linked to 4chan overnight.

The firm's website was brought back online at about 10.45am, following a Distributed Denial of Service (DDoS) strike.

It follows similar action against music and film industry websites over the weekend under the auspices of "Operation: Payback Is A Bitch", coordinated over IRC by members of 4chan, the anarchic message board.

Andrew Crossley, the head of ACS:Law, told The Register the attack was "typical rubbish from pirates".

"Big whoop," he added.

"It was only down for a few hours. I have far more concern over the fact of my train turning up 10 minutes late or having to queue for a coffee than them wasting my time with this sort of rubbish."

ACS:Law obtains court orders to force ISPs to reveal the identities of customers linked to IP addresses observed sharing copyright files in BitTorrent swarms. It then sends letters demanding payment of several hundred pounds to avoid a civil lawsuit.

The files are typically video games or pornographic films, with copyrights held by Digiprotect, a specialist German monitoring firm that aims to profit from piracy. ACS:Law does not usually take anyone who refuses to pay to court, however, and is currently under investigation by the Solicitor's Regulatory Authority. A tribunal is expected next year.

Crossley claimed this morning that the only victims of the DDoS attack were the targets of his letters. "We provide an awful lot of resources to help people," he said.

ACS:Law joins the MPAA and RIAA as a brief casualty of "Operation: Payback Is A Bitch". The BPI, which was also targeted, managed to stay online.

The attacks have been linked to Anonymous, an ad-hoc activist group that came to prominence via 4chan as an anti-Scientology campaign. ®