FDF File Spam is on the rise

Martin Brinkmann
Sep 8, 2007
Updated • Mar 16, 2014
Email, Security

If there is one thing for sure it is that spammers are creative in finding new ways to bypass anti spam filters. They send distorted pictures, add random text to their messages, zip or password protect spam, use excel files, pdf files and nowadays fdf files. Fdf files? What's that again?

Adobe Fdf is the file extension for the Forms Data Format which I'm sure most of you have never heard of before -- I have not.

The real beauty of the format for spammers is that the Adobe Reader is able to open and display the contents without problem. A great way for spammers to provide everyone with up to date news of stock market insider tips without having to rely on camouflage tactics to bypass spam filters.

The best way to handle this sort of spam is to create a new spam filter that would move mails with an .fdf attachment right into the junk folder. No company that I know of is sending .fdf files to their customers which means that it is 100% save to automatically move them to the junk folder.

Obviously, if you do receive fdf files by mail occasionally, you may want to whitelist the senders of those legitimate files to make sure they do not land in junk.

Update: Users who do not make use of Adobe Reader should be safe as well, as the majority of third party readers is not supporting Adobe's fdf file format. Viable alternatives are Nitro PDF Reader, Foxit Reader or the bare-bones reader Sumatra.

These alternatives are often a lot faster when it comes to opening pdf documents on the system, which is one of the reasons why many experienced users install them and not Adobe Reader.

The take away from this article is the following: Spammers may use lesser know file formats to send their spam messages to users. The majority of Internet users know that they should not open .exe files that are send to them.


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  1. Opus said on January 21, 2019 at 7:15 pm

    Sysdane is using .fdf files for “coupons” (the eye drops). Not sure of the outcomes of actually trying to open one of these .fdf files. I stopped when Acrobat brought up a notice that the “form” was trying to contact a web site.

  2. Tony S said on September 18, 2007 at 10:34 am

    All those different spamming techniques are just creative ways for spammers to avoid being red flagged by spam filters. Anti spam software vendors should be equally creative and innovative to provide proactive solutions to block those annoying e-mails. Bayesian filtering is one of the best features to look for when purchasing anti spam solutions. For anyone looking for more information related to different spam types, you can go to http://www.gfi.com/whitepapers/attachment-spam.pdf – it’s a free whitepaper that can give you a good overview of the different spam techniques. Definitely a great read!

  3. gnome said on September 8, 2007 at 1:28 pm

    Pesky little spammers…. Bah!

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