This article and this search suggest that the 32-bit word 0x41414141 is associated to security exploits.

Why is 0x41414141 associated to security exploits?

It's nothing fundamental.  It's just a historical convention, like using foo as the name of a variable when you have no clue what to name it.

In more detail: The simplest way to test for a buffer overflow is to type a long string of A's (AAAAAAAA...) into a text field, and see what happens.  If the program crashes, it might be vulnerable.  If the program crashes and a debugger shows 0x41414141  in the program counter, ooh boy, you hit pay dirt: the program is almost surely vulnerable. (Remember, the ASCII code for 'A' is 0x41 in hex, so 0x41414141 is what you'd see if you looked at the byte-level representation of a string of A's in a hex editor.)

Why A's?  No reason at all; they're just the first letter in the alphabet.

So, this is a quick-and-dirty test that pentesters sometimes use.  But of course, there's nothing special about 0x41414141.  Douglas Adams fans could type in a long string of B's, and then look for 0x42424242.  That'd be equally effective, and even more fun.  I gotta remember to use that one in my next hacking demo.....
