whatever can be a virus. It depends on what the application does, how the application warn user about its behave and so on. Its not a particular technique that make a virus but the behave of the application.
Is the car that invest the pedestrian or the car driver?
And more (you shoul know this one ) it's the paiter or the brush that make the picture?
To go tecnical, MC_Eval does nothing. It just transform a more human way to write bytes into bytes.
MC_Exec just load the sequence of bytes into a string, calculate the string pointer and make an execution jump to that pointer. This technique is used thousands of times per seconds by any switched on PC. Nothing more.
DEP protection is interesting and to be used if needed. We already talked about it in other threads because there were some problems with thinAir. We solved that problems and to avoid those problems again, since than Roberto works with DEP switched on: "/noexecute=optin" in BOOT.INI file.
What I can think is a way to warn user if MC_* functions are used inside a script. Something like VBA macros protection.