Spam emails reached nearly 70 percent of all emails sent during August despite the decline of PDF spam, according to Symantec.
Symantec's monthly spam report for August said unsolicited email accounted for 69 percent of all email sent, up 3 percent from July. Spam volumes are creeping up toward the levels reached last October when image spam - spam messages embedded in image files that spam filters initially couldn't read - inflated junk mail to 73 percent of all messages sent.
In August, image spam had little impact, accounting for less than 10 percent of all spam sent, according to Symantec.
Last month also saw the dramatic rise of PDF spam, email messages with a PDF attached - which most spam filters can't read - that usually attempted to convince the recipient to purchase stocks. First spotted by Symantec in June, PDF spam accounted for 20 percent of all spam at its peak in mid-August.
Spammers quickly retreated from the technique, however, bringing its end-of-the-month level to less than 1 percent of all spam.
Symantec's take is that spammers have backed off from sending PDF spam to tweak the technique - in essence reloading their spam blasters - or have decided this form of spam isn't working and have gone back to the drawing board.
Officials at Sophos, another security vendor, agreed with the theory that PDF spam was more trouble than it was worth for recipients - since they had to actually open an attachment to read the message - and so spammers weren't getting the desired results from the technique. Sophos says that email users are hesitant to open email attachments from unknown senders.
August also was a big month for e-greeting spam, messages that point recipients to a website where they promise an electronic greeting will be waiting - but malware is downloaded. There was also a spam blast that promised to bring recipients to the popular YouTube site to see a video of themselves, but instead linked them to a malware-laden site.
Both these blasts were powered by the Storm worm.