In the wake of the latest PDF / ZIP spam surge, many security analysts and vendors have taken a shot at explaining this phenomenon. It is the case of GFI Software who released an interesting whitepaper called “Attachment spam – the latest trend”.

Image spam is a moving target because spammers frequently change their spamming tools as well as the content and format of their messages, so you cannot rely on one technique to detect them all.

In this post I will present some of the most popular RBL / DNSBL services (free and commercial) as well as things to consider when using a RBL service .

In case you use Adsense, YPN or Chitika you might be intersted in AdsBlackList.com’s free service which lists hundreds of worthless websites URL that you can filter not to appear on your website.