Data Execution Prevention (DEP) helps prevent damage from viruses and other security threats that attack by running (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.
Unlike a firewall or antivirus program, 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 microprocessors 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.
DEP can take advantage of software and hardware support. To use DEP, your computer must be running Microsoft Windows XP Service Pack 2 (SP2) or later, or Windows Server 2003 Service Pack 1 or later. DEP software alone helps protect against certain types of malicious code attacks but to take full advantage of the protection that DEP can offer, your processor must support "execution protection". This is a hardware-based technology designed to mark memory locations as non-executable. If your processor does not support hardware-based DEP, it's a good idea to upgrade to a processor that offers execution protection features.
Click start, right click my computer, click properties then advanced, click settings on performance then data execution to change the way it runs