According to iTnews, PDF spam is on the fall. Hmm...that sure was a short lived attempt by spammers to increase stock prices. Paul Ducklin of Sophos claims that PDF spam is dying out because it requires more user interaction than regular/conventional spam and is therefore not as successful as its predecessor (oh wait! Regular spam is still around). I think we all agree with him when he says that PDF spam has been around for a while now but in the last couple of months, it has gone from being a rare occurrence to almost replacing the usual (read: monotonous) spam. The failure of PDF spam due to a higher requirement of user interaction is actually a blessing for both sides. Spammers might (most likely) start focusing on releasing new types of spam with as little user interaction as possible. I really don't think there is a much easier way to spam people other than the conventional method but that is no excuse to take this issue lightly. Until we start experiencing a fairly large drop in inbound PDF spam, we assure you that our Software Development Team is constantly working on it.

By the way, BtoBonline.com has an excellent description of what is considered spam (based on the CAN-SPAM Act). I'm sure you won't be disappointed.