Spammers Prefer Compromised Accounts To Botnets
Orome1 writes "Spammers today favor compromised accounts for sending spam, gradually shifting distribution away from botnets, according to Commtouch. The changed tactic has emerged as spam levels dropped dramatically, following several high-profile botnet takedowns. Spammers are now using a combination of malware and phishing to compromise legitimate accounts and then using these accounts to send low-volume spam outbreaks."
All of the major spam filters use reputation as a metric. And stealing reputation is easier than building it.