Spam attaches a PDF file to the image spam

One of the latest spammers' tricks is to use the PDF format to infiltrate mailboxes because the e-mail filter cannot read the contents.

Image spam (image files with .gif or .jpeg files with promotional content inserted immediately in the content) are used by spammers for over a year and have been very successful. But when the security tools were upgraded to deal with this situation, spammers continued to play "cat and mouse" and two months ago, they launched a new trick.

Attaching PDF files is a wise move because users still think the advertising message will have to appear immediately in the body of the e-mail. Furthermore, the PDF format is currently popular in transactions, so the recipient needs to open the file due to concerns about missing important information. According to Symantec security firm (USA), PDF spam accounts for 8% of total spam in July.

Meanwhile, British firm Sophos found that PDF spam began to appear in "pump-and-dump" spam campaigns - a form of "blind burning" to manipulate stock prices of companies and victims. The latest is wireless product maker Prime Time Group (PTG).

Earlier this week, Internet users continuously received e-mail containing PDF attachments with content that attracted them to buy PTG shares. Investors may not realize that the other spammers hold a large amount of shares at cheap prices and are mobilizing people to buy and sell to pump high prices. After that, they will sell all those shares to make money (pump and dump). The spammer succeeded when global spam increased by 30% in one day and the price of PTG shares also increased by 60%.

Sophos "pump-and-dump" spam estimates currently account for about 25% of global spam. In April, IDC reported that about 97 billion e-mails were sent each year, of which 40 billion were spam.