PDF spam has returned. According to management services vendor MX Logic, PDF spam accounted for .5% of all spam volume last week.

"It could be somebody testing the waters or it could be the calm before the storm," Sam Masiello, Director of Threat Management, said. "Generally your smaller, more localized attacks are less likely to be detected, but in this case it was obvious based on the subject lines that it was suspicious."

PDF spam first hit the radar in July, thanks to the Storm Worm, and pitched pump and dump stock schemes. This new wave of PDF hawks various pharmaceuticals. It's not yet known if this new wave of PDF spam is related to Storm.