Swedish telco Telia Sonera has shut down the internet connections of Latvian company Real Host after it was linked with the world's biggest cybercrime botnet.
Real Host has been compared to McColo and Atrivo, two hosting companies shut down by authorities because of links to large-scale cybercriminal activities.
Security researcher found that Real Host had rented a large range of internet addresses from a server provider in Riga called Junik and was linking to the internet through Telia.
The researchers found that Real Host's servers had captured around 3.6 million PCs for use in a botnet called Zeus.
Zeus has been linked to Rock Phish, a Russian-led gang blamed for half of the world's phishing attacks to steal credit card and banking information.
Some Real Host sites tried to infect visitors through only recently patched security holes in Adobe Flash, while others sold stolen banking data or recruited people to transfer money into accounts controlled by cybercriminals.