August was a busy month for spammers, with junk e-mail levels reaching nearly 70% of all messages sent -- despite the quick decline of a new type of spam.

According to Symantec’s monthly spam report for August, unwanted e-mail accounted for 69% of all mail sent, up 3% 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% of all messages sent.

In August, image spam had little impact, accounting for less than 10% of all spam sent, according to Symantec.

Last month also saw the dramatic rise of PDF spam, e-mail 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 % 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% 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, agree 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 e-mail users are hesitant to open e-mail attachments from unknown senders.

August also was a big month for e-greeting spam, messages that point recipients to a Web site 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.