European spam networks have pumped out more unsolicited mail than the US for the third month in a row, according to a recent study.
The study, commissioned by security vendor Symantec, called this a "significant shift" in spam trends as, historically, compromised US computers have been used to send spam mail, and many spammers have been US-based.
Fredrik Sjostedt, one of Symantec's European product marketing managers, told ZDNet.co.uk on Tuesday that Symantec suspects gangs are taking advantage of the increasing European broadband market.
"The penetration of broadband is tremendous in Europe," said Sjostedt. "We've now clearly overtaken the US in sending spam."
Symantec also believes many spammers are now based in Europe. "Historically the majority of spammers were US-based, but now we're seeing a lot of Eastern European and Russian spam gangs active. Spammers tend to use closer turf as a jump off point."
More broadband means compromised computers can send spam faster, while gangs are increasingly becoming organised, said the Symantec manager.
"We've moved away from traditional, individual spammers, to loosely tied groups of spam senders, malware coders, and people selling access to botnets," said Sjostedt.
The largest botnet sending spam is Storm, said Sjostedt. Storm is a network of compromised computers with sophisticated attack and defence mechanisms, including "fast-flux" command and control servers, which frequently change location.
"Storm is the most prevalent distribution method [for spam]," said Sjostedt. While most spam relays are in Europe, botnets are global phenomena, Sjostedt pointed out.
