
The gang is reported to have sent emails directing users to forged Poste Italiane websites designed to steal log-in information. Poste Italiane is a government-owned postal service which also offers financial services.
More than 10,000 web pages based in Italy had been attacked by the hackers in July alone to harvest account details for identity theft.
Yuval Ben-Itzhak, chief technology officer at security firm Finjan, said that the arrests represent a major milestone in stamping out the problem of organised crime on the internet.
"Phishing is a very pervasive problem, as many of the emails and websites do look quite genuine," he said.
"Companies and consumers should consider installing website security analysis software to counter this type of internet fraud."