Two people suspected of involvement with the notorious Zeus banking Trojan have been arrested in Manchester.
A man and a woman both aged 20 have been arrested on suspicion of involvement with a banking Trojan thought to have infected thousands of computers worldwide.
The pair, who were not named, were bailed until March 2010 pending further enquiries.
The Zeus Trojan stole banking details from the computers it had infected, as well as passwords.
"If the police have made a positive step in unravelling the gang behind Zbot then that will be very good news for everyone interested in making the internet a safer place," said Graham Cluley of security firm Sophos.
Cluley said that Zeus, also known as Zbot, hijacked computers and used them to send out more malware.
"Zbot hijacks your computer, making it part of a criminal botnet. Hackers control thousands of compromised computers around the world - using them as a zombie army to spew out spam, spread more malware and launch denial-of-service attacks," he said.