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New Spammer Tricks Thwarting Filters
By: Sharon Khare   |   Nov 16, 2006
SpamStopsHere, provider of e-mail security and spam filtering solutions, has said that new sophisticated spammer tricks are thwarting spam filters and spam has risen by more than 50 percent in just the two months since September 2006. More significantly, it is not just more of the same old spam, but radically new methods that are challenging, and in many cases defeating existing anti-spam systems.

In the new type of 'image spam', the image in each spam message is altered with randomized pixels to defeat image checksums; even the image size is randomized, as is the text. Image spam was initially seen in penny stock spams, but due to their success in defeating anti-spam systems, they are now pitching 'the usual' products.

Most anti-spam systems rely heavily on IP Reputation or IP Blacklists, which accept email from trusted mail servers, e.g. from legitimate companies, and block emails from known spam sources. A new spam trick is to not send the spam directly to the intended recipient, but to bounce it off the mail server at a legitimate company. This is done by forging the To: and From: fields and finding mail servers that bounce the entire email message. The recipient then receives a 'Non-deliverable' email message, and when opened, sees the spam. Since the spam came from a legitimate company's mail server, it is difficult for an IP-based anti-spam system to block without also blocking legitimate emails from that company.

Further complicating things, some spammers have already used both methods—bouncing highly randomized image spam off of legitimate mail servers. After receiving such spam, many users have mistakenly accused innocent victims of sending the spam.

Ted Green, president, Spam StopsHere, said, "We don't rely much on IP address reputation, but instead fully scan each email message for the 'Click me' links found in traditional, non-image spam. It doesn't matter if it is sent directly or is bounced, we block it". To block image spam, SpamStopsHere analyzes all emails containing images coming to its thousands of customers and automatically determines the 'template' from which an image spam is randomized. Once confirmed by its technical staff, all image spams matching a known template are blocked.

SpamStopsHere claims to block over 99 percent of traditional spam and 98 percent of image spam, while keeping mistakes with legitimate email to 1 in 100,000.
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