PC World — Spam volumes jumped 8 percent today thanks to a major spam outbreak that filled inboxes with a professional-looking .PDF attachment touting the stock of a German-based company. According to Ironport Systems, this is the first time Adobe PDF attachments have been used to deliver stock spam.

The spam e-mail promoted Talktech Telemedia, a German-based firm with penny stock on the Frankfurt exchange. The spam boosted the company's stock 20 percent from 30 cents a share to a daily high of 36 cents a share. Here is a copy of the spam PDF attachment.

"This is an unprecedented volume of spam," says David Mayer, an IronPort spokesman. He estimates 5.4 billion copies of the spam e-mail were sent out by "botnets," armies of compromised PCs enlisted by cybercrooks to send spam or distribute malicious software.

Wednesday's spam outbreak fooled many antispam companies, Mayer says. That's because spam filters don't look for PDF attachments that contain spammy messages. In the past, stock spam has been sent as either e-mail text promoting a company or as an image of text that promotes a company's stock. Today, most antispam firms have grown wise to image spam and block it. E-mails harboring spam messages in PDF attachments are a different story, Mayer says.

"We have never seen anything like this before," Mayer says. A PDF document, he says, promoted the stock of Talktech Telemedia. At first glance the PDF looks legitimate, which is likely why the firm's stock rose in price nearly 20 percent and why ISPs failed to block the e-mail.

"We are definitely going to be seeing a lot more of this type of spam," Mayer says.

Stock spam is sent by spammers who buy shares of a penny stock company and use massive spam e-mailings to drive up the price of the stock. When the stock grows in value, the spammers sell the stock for a profit.

In March, the U.S. Securities and Exchange Commission suspended trading for 35 companies that allegedly benefited from spam e-mail campaigns to hype their stocks.