Data Execution Prevention (DEP)

Data Execution Prevention (DEP) helps prevent damage from viruses and other security threats that attack your computer by running (sometimes called executing) malicious code from memory locations that only Windows and other programs should use.

This type of threat causes damage by taking over one or more memory locations in use by a program. Then it spreads and harms other programs, files, and even your e-mail contacts.

This type of "attack" is very common and that is why Microsoft have introduced DEP into Service Pack 2 for Windows XP..

Unlike a firewall or antivirus program though, Data Execution Prevention DEP does NOT help prevent harmful programs from being installed on your computer. Instead, it monitors your programs to determine if they use system memory SAFELY. To do this, DEP software works alone or with compatible processors to mark some memory locations as "non-executable". If a program tries to run code - malicious or not - from a protected location, DEP closes the program and notifies you with an warning message..

Software or Hardware DEP?

There are two types of Data Execution Prevention "Software Enforced" and "Hardware Enforced".

Most users reading this article are going to be using Software Enforced data execution prevention - which is available to any machine running Windows XP Service Pack 2.

Hardware enforced DEP is only available (as of writing this article) to users who have machines based on the AMD Operton 32 or 64 bit processor, or the AMD Athlon 64 processor with NX (no execute page protection), or the Intel Itanium processor with XD (execute disable bit).

Where Can I Find DEP On My PC?

1. On the My Computer icon right click with your mouse and choose Properties. (My Computer can be found on the desktop and/or the Start menu depending on how you have your Windows XP setup.)

2. A small window will have appeared called: System Properties. Look for the "tab" along the top called Advanced, now click it.

3. Now look for the section called Performance and click the button called Settings.

4. You will now see a new window appear called Performance Options, click the tab along the top called Data Execution Prevention and you should get the same window view as the image below.?

Fig 1.1 - The DEP tag of the Performance Options Window.

By default Data Execution Prevention is turned on for Windows programs and services only and for most users this is fine.

However, you can gain more protection by selecting the second option and DEP will now work for ALL programs and services on your computer. BUT this is know to generate some error messages as legitimate software can conflict with DEP.

If this happens, you get a warning dialog box on your screen informing you of an error and the software you are trying to use will not start.

If this was a nasty piece of software lurking on your computer then DEP will have done its job. BUT if it happens to you when trying to work with some software you fully trust, this can be a problem, but fortunately there is a solution...

...you will need to tell Data Execution Prevention to ignore the software you want to use!

(Note: The DEP error message should always tell you which software caused the problem and who the publisher is, if you do NOT recognise the information provided then suspect fowl play and seek the advice of a more experienced user/technician....)

Enabling this option can ALSO cause a conflict with some Hardware drivers and present you with a warning dialog saying something along the lines of:

 (ATTEMPTED_EXECUTE_OF_NONEXECUTE_MEMORY).

If that happens you will need to try and track down updated Windows XP drivers for the Hardware involved - preferably marked "Digitally Signed" for Windows XP

To find out how to tell Data Execution Prevention to ignore the software you want to use read this page:

http://www.updatexp.com/dep-exceptions.html

To find out how to update a hardware driver read this page:

http://www.microsoft.com/windowsxp/using/helpandsupport
/learnmore/russel_02october14.mspx 

I hope this article on the Windows XP Data Execution Prevention (DEP) was useful?