Security vendors warn <A HREF="http://www.eweek.com/article2/0,1895,2160212,00.asp?kc=PBPWUEMNL071907EOAD">image spammers are increasingly using PDF files</A> to bypass spam filters. Researchers at BorderWare Technologies, based in Toronto, reported that on any given day more than 30 image spam campaigns are being run, with more than half of those being PDF-based.

The findings come as a number of vendors have reported that the amount of image spam has declined in favor of PDF spam. A Commtouch report for the second quarter of the year found that image spam had dropped to less than 15 percent of all spam, compared with 30 percent in the first quarter of 2007.