For quite some time spammers have been trying to hide links advertised in their e-mails. The main reason for this is probably increasing effectiveness of various realtime blocklists, such as SURBL. For those that aren’t familiar with SURBL (http://www.surbl.org), it’s an RBL that lists list URIs found in spam e-mails. In other words, instead of listing spam zombies or relays, RBLs like SURBLs list sites that are referenced in advertised spams.

Anti-spam applications generally query multiple RBLs and latest versions of Spam Assassin, the most popular open source anti-spam application, will query SURBL by default.

Spammers realized that this can cause them big problems so initially they started using various open redirectors. Redirected URLs try to hide themselves behind some other (innocent) domain and server. For example, Google has a redirector service that can be easily used… DShield; Cooperative Network Security Community - Internet Security - dshield

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