According to Microsoft, "DEP is a security feature that can help prevent damage to your computer from viruses and other security threats. DEP can help protect your computer by monitoring programs to make sure they use system memory safely. If a program tries running (also known as executing) code from memory in an incorrect way, DEP closes the program."
By default, DEP is set to monitor only essential Windows programs and services. You can, however, increase the protection provided by DEP by setting it to monitor all programs and services.
How to confiure DEP to monitor all programs and services
Click Start > Control Panel > System and Maintenance > System and enter your administrator password if prompted. In Peformance, click Settings > Data Execution Prevention. Check the option Turn on DEP for all programs and services except those I select click OK and reboot.
DEP has now been set to monitor all applications and services.
Should an application stop working after you have made this change, you should ideally see whether there is a vendor update available that will remedy the problem. Should no update be available, a less secure workaround is to simply exclude the application from DEP's monitoring. To exclude an application, navigate your to the Data Execution Prevention tab, click Add, browse the the problematic application's executable and click Open. DEP will no longer monitor that application.
If you are running a 64-bit edition of Windows, you will not be able to opt any 64-bit application out of DEP. Should an application stop working after you have set
DEP to monitor all applications and services, your only option will be to either cease using that appliation or revert to DEP's default settings. Note that this will not be a problem with 32-bit versions of Window which do enable you to opt either 32-bit or 64-bit application out of DEP's monitoring.