Avalanche: Online crime network hit in global operation

More than a million emails were sent every week with malicious content, Europol said

One of the world's biggest networks of hijacked computers has been dismantled after a four-year investigation, the EU law enforcement agency Europol says.

The Avalanche network was used to target online bank customers with phishing and spam emails, it adds.

More than a million emails were sent per week with malicious files or links. When users opened them, their infected computers became part of the network.

Five people have been arrested, but Europol has not said where.

According to Europol's statement:

• The operation searched 37 premises and seized 39 servers, supported by investigators from 30 countries

• The network was estimated to involve as many as 500,000 infected computers worldwide

• Victims have been identified in over 180 countries

• Damages in Germany alone ran to 6m euros ($6.4m; £5m)

• Estimates of losses worldwide are in the hundreds of millions of euros, but exact figures are difficult to estimate

The investigations started in 2012 in Germany, after a substantial number of computer systems were infected, blocking users' access.

Millions of private and business computer systems were also infected with malware, giving criminals access to email and bank passwords.

The announcement comes after a cyber attack left 900,000 Deutsche Telekom customers with their broadband service cut off on Sunday.