Fighting spam, phishing, and online scams at the network level

Recent estimates indicate that upwards of 90% of all email traffic is spam [4]. Spam is more than just a nuisance: it consumes resources on the network and at mail servers, and much of it is also used to mount attacks on users via malware and social engineering attacks (e.g., phishing). In recent years, spammers have increased their virulence, by sending spam from large collections of compromised machines ("botnets"), encapsulating their messages in content that is difficult to filter (e.g., images), and by targeting their messages towards specific groups of users. Indeed, spammers show no sign of slowing, and, worse, their techniques may carry over to other domains (e.g., VoIP, mobile devices) in the future.