Themida is a way of encrypting your work... Look at it this way, say you have the text "I like cheese", anyone can see it in your project if they open it in oly or a hex viewer. So what themida does is change the the way we look at it (its the same code, and does the same thing, but its all "scrambled" and less likely to be open/detected). So we now have "#@$JKASDJ#)@$*" or somthing from our "I like cheese," but don't try to just change things in oly because everything that is being changed is being linked back by the engine to the original code so it knows what "#@$JKASDJ#)@$*" means