I have been getting this error message, data execution prevention, why?

When I go to My documents/my pictures and I try to do anything with my pics, I get a box that comes up and says Data Execution Prevention-microsoft windows

to help protect your computer, windows has closed this program.

Name windows explorer

publisher microsoft corporation.

This is a new problem for me and it's anoying. Is there anyway to fix this?

I am running windows XP, sp2, and it's a DELL.

I am using avast virus protection, CCleaner, ad-aware, spybot search %26 destroy and window washer. I did a defrag and a disc cleanup.

I must say that it worked fine before I went on vacation and when I got home it was doing this. My son used the internet while he was here with the cats. Other than that, i don't know what is going on.

I have been getting this error message, data execution prevention, why?pc security

Data Execution Prevention (DEP) is a set of hardware and software technologies that perform additional checks on memory to help prevent malicious code from running on a system. In Microsoft Windows XP Service Pack 2 (SP2) and Microsoft Windows XP Tablet PC Edition 2005, DEP is enforced by hardware and by software.

The primary benefit of DEP is to help prevent code execution from data pages. Typically, code is not executed from the default heap and the stack. Hardware-enforced DEP detects code that is running from these locations and raises an exception when execution occurs. Software-enforced DEP can help prevent malicious code from taking advantage of exception-handling mechanisms in Windows.