The Next Generation of Spam: Image and PDF Spam

As spam filters get increasingly effective, spammers are changing their tactics to foil anti-spam software and get through to your inbox. Recently, this has involved a shift from the use of text-based spam to the use of embedded images and PDF file attachments as the preffered delivery method for their spammy intrusions.

Image Spam

The prevalence of this form of spam increased in 2006, primarily as a means for advertising penny stocks. It involved the use of a picture or graphic embedded in the body of the junk email. The junk email's message is displayed as an image.

Because most anti-spam filters are text-based, image spam was relatively successful. This led to its use in advertising everything from sexual enhancement to fake pharmaceuticals.

One serious effect of image spam has had is to further clog up Internet bandwidth, and drive up costs to businesses. This is because the average size of each junk email almost doubled. In fact, this increased size and the sheer volume of image spam forced many businesses to block all emails that contained embedded or attached images.

By early 2007, image spam reached an all-time high, accounting for almost two-thirds of all junk email. However, as spam filter technology has adapted to detect image spam, its use has since declined to less than 15% of all junk email. Instead, spammers are turning to PDF spam
  
PDF Spam

Spammers are increasingly using PDF files to bear their spam messages. The practice begun in mid-2007, primarily as a scam to fool recipients into investing their money in the stock of a particular company.

With this type of spam, the junk email is sent out with a PDF file attachment, which most anti-spam filters cannot or do not read. These attachments range from rudimentary to professional-looking documents. The text in the body of the email is usually nonsensical gobbledygook that the spam-filter does not recognize as junk mail.

For the spammer, the use of PDF files is advantageous because PDF files are so commonly used in the business world. In fact, several companies allow or even require their business email systems to deliver these documents to the recipient. This makes it very likely that this PDF spam will reach the user's inbox.

The use of junk mail with PDF attachments takes up even more Internet bandwidth. This is because PDF files are generally much larger than the embedded pictures and graphics used in image spam. Image spam is typically in GIF format; PDF files are upto 3 times the size of these files.

The upside to the use of image and PDF spam is that so far, there is no hard evidence that either one can be used to embed malicious software on the recipient's computer. The only harm is done to those who do what the message says. Spammers have also begun to experiment with attachments in different file types such as excel and zip files.

The advent and decline of the different types of spam attest to the cat-and-mouse game that goes on between the spammers and the security experts. As anti-spam technology catches up to their techniques, they continue to innovate and change tactics to deliver their spam messages.

Top Ten Tricks of the Spammer

Top Ten Tricks of the Spammer

The spammer's most fervent hope is that you are ignorant of the tricks and tactics used to spam your inbox. Learning the spammer's nefarious ways is your best protection against spam.

Manipulating Text:

This is one of the most commonly used spamming techniques. Spammers will manipulate the text in the email, to foil the anti-spam filters. They may, for example, deliberately misspell some words: "M0rtg4ge" for example. They may add characters or spaces to words in the email header, to make the email seem unique from other email. Like this: X_A_N_A_X Here's an example, . They may also insert random strings of text within the email.

Chain Letters:

Spammers may send out chain letter instructing you to forward the email to your friends and family. To entice you to do so, it may claim that forwarding it will bring good luck. This spam may carry viruses or a Trojan horse, which is sent along to anyone you forward the email to.

Image-based Spam:

The spammer sends out spam that contains an image in GIF format. This image bears the spammy message. Image-based spam is effective in by-passing spam filters because they are generally text-based.

Dictionary attacks:

This is a technique used by the spammers to find email addresses that they can spam. It involves trying random combinations of common names and words, and using these to making up email addresses, e.g. JaneDoe@YourISP.com, JDoe@YourISP.com, JaneDoe1@YourISP.com. The spammer will then send out junk email to the different variations of these addresses in the hope that some of it will go through,

Spammers tend to direct the dictionary attacks at the large email companies, which have a large number of customers. 

Email spoofing:

Email spoofing involves the use of a fake email header that is written to make it look like someone other than the spammer sent the email. Very often, the spammer will make it look like the email came from a credible source such as your bank or yahoo, and try to get you to reply with personal information such as a password, social security number or credit card number. This technique is widely used because it is easy to do, and tends to catch the recipients off guard.

JavaScript:

The spammer can use Javascript that will ensure that the spam is only visible when the email is loaded. This type of spam can only be prevented using anti-spam software that decodes or blocks the java script.

Social engineering:

This spammer ploy attempts to fool the recipient into reading the junk email by pretending to be an acquaintance. It involves a junk email that has a "personal" subject line, such as "I'm leaving tomorrow," "I got your message" or "Let's meet again".

Mining message boards and chat rooms:

When you post a message to a message board or chat room and leave your email address, automated programs called spambots will find your address and add it to the spammer's mailing list. Much like a listed phone number in the telephone directory, leaving your email at these types of websites makes it public information.

Web beacons:

A web beacon, also called an "invisible GIF," is an image sent out with spam that is invisible to the recipient. When the email is opened, the spammer will be alerted that your email address is "live."

Open proxy, 3rd-party servers:

An open proxy is a third-party server that enables the spammers to camouflage their real identities as well as their Internet locations, when they send out their junk mail. Many spammers use these open proxy servers to help maintain their anonymity.