PDF spammers getting creative

PDF spammers have started varying attachments to fool spam filters, security vendor MessageLabs has warned.

After appearing only a few months ago, the PDF phenomenon now accounted for 20 percent of the image spam passing through the managed service provider's network, the company said. In the last fortnight, however, new types of modified PDF spam had started appearing.

Spam filters had now adapted, turning PDFs from a document and attachment type automatically trusted into one that was now being filtered by antispam engines, causing the spammers to send out new, altered types of PDF. Techniques included altering the rendering size of PDFs, introducing pixel changes to make PDF blocking using signatures impossible, and adding random text within PDFs.

PDFs were also turning up with security features such as encryption turned on, another feature that made it hard to scan within a document to single out spam from genuine PDFs. The overall aim was to generate so many unique PDFs that antispam engines would be overwhelmed.

"This is almost certainly being automated by bots," said Mark Sunner of MessageLabs. "It will eventually be used in conjunction with social engineering techniques," he added, referring to targeted PDF attacks where real people were sent documents from known contacts.

According to Sunner, the advantage of a managed service company such as MessageLabs was the ability to detect rogue PDFs by analyzing information such as IP source. A corporate gateway would not be able to do this because only the ISP itself would be able to see this information with any degree of reliability. "Where the PDF is coming from can also indicate a problem," he said.

In recent time, third-party systems for verifying the senders and contents of PDF documents have started to appear, including one from Geotrust that takes advantage of Adobe's Livecycle Document Security server.

Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

John E. Dunn

Techworld.com

Comments

Comments are now closed.

Most Popular Reviews

Follow Us

Best Deals on GoodGearGuide

Shopping.com

Latest News Articles

Resources

GGG Evaluation Team

Kathy Cassidy

STYLISTIC Q702

First impression on unpacking the Q702 test unit was the solid feel and clean, minimalist styling.

Anthony Grifoni

STYLISTIC Q572

For work use, Microsoft Word and Excel programs pre-installed on the device are adequate for preparing short documents.

Steph Mundell

LIFEBOOK UH574

The Fujitsu LifeBook UH574 allowed for great mobility without being obnoxiously heavy or clunky. Its twelve hours of battery life did not disappoint.

Andrew Mitsi

STYLISTIC Q702

The screen was particularly good. It is bright and visible from most angles, however heat is an issue, particularly around the Windows button on the front, and on the back where the battery housing is located.

Simon Harriott

STYLISTIC Q702

My first impression after unboxing the Q702 is that it is a nice looking unit. Styling is somewhat minimalist but very effective. The tablet part, once detached, has a nice weight, and no buttons or switches are located in awkward or intrusive positions.

Latest Jobs

Shopping.com

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?