A security firm has criticised the UK courts for inconsistent sentencing of cyber-criminals after a Fathers 4 Justice campaigner who admitted hacking a website and distributing viruses was spared a jail sentence.

Matthew Byrne, 38, from Nottinghamshire, has been given an eight-month sentence, suspended for two years, after pleading guilty to writing the Mirsa-A and Mirsa-B viruses which posed as messages from the Fathers 4 Justice campaign group.

He also admitted hacking into accounts belonging to users of dating website Loveandfriends.com.

"The Computer Crime Unit at Scotland Yard should be congratulated for bringing another hacker to justice, but we must question whether the legal system is dealing with virus writers in a consistent fashion," said Graham Cluley, senior technology consultant at Sophos.

"In 2003, 21 year-old Welsh virus writer Simon Vallor received a two-year jail sentence from the same judge, and more recently the British government has approved the extradition to the US of alleged Nasa hacker Gary McKinnon.

"Is there a danger that conflicting messages are being sent to the hacking community by allowing Byrne to escape jail?"

Byrne left a clue buried inside the W32/Mirsa-A virus stating that 'Sheffield Hallam university is corrupt'.

"It was a stupid message for Byrne to include inside his worm. Sure enough, at the time of his arrest, he was living in Sheffield," said Cluley.