I've been running Windows 7 Professional (x64) for some time now, and one of the security features I only just recently learned about is Data Execution Prevention. I checked to see if DEP was enabled or not, and found that it must've set itself to "Turn on DEP for essential Windows programs and services only". I'm thinking about setting it to "Turn on DEP for all programs and services except those I select", but I'm concerned about system stability.
I've read that DEP can crash a great number of programs, and that it's typically unclear that DEP causes the crash at the time, leaving the user to wonder what happened. I know that exceptions can be made, but I'm worried, because I don't necessarily know every executable that each program uses in every situation. For example, I recently learned that Steam (which I use often!) has problems with DEP. Additionally, Steam updates itself automatically by spawning a program called SteamServiceTmp.exe, which it deletes after patching the main Steam executable. If SteamServiceTmp.exe causes a DEP problem, I doubt I'd realize it, particularly since the executable doesn't technically exist on the machine. If something similar happened for another program, I'd be way clueless about it. If it crashed my antivirus (NOD32 v4), I'd be in big trouble, too.
So, short story: How can I expect DEP to impact my system stability? Is it a good idea to turn it on? Is it a bad idea to turn it on after running for months in the "Turn on DEP for essential Windows programs and services only" mode? Thanks!