first of all, lol at the "deep web". why did it suddenly become fashionable to call tor the deep web? f***ing 4chan kids, +fravia writes one article on the deep web, now anything that requires more than 5 seconds to access is the "deep web". has anyone found anything useful on tor anyway? all that I've been able to find are crappy hacking forums full of newbs, people trying to buy drugs, and links to kiddy porn.
ahem, sorry for the digression. if you want to sell a 1337 RAT to kiddie forums then you should do it in C# or VB6, but if you want it to actually be good it should be a combination of C and assembly. if you know python that will ease the transition into C, and knowing C will ease your transition into assembly. aside from languages, you'll also need to have a good understanding of the API of your target system (probably linux or windows), and to understand some low-level aspects of the architecture (probably x86). but again, if you just want to stitch together snippets of code into something easily slapped together with, most importantly, a pretty gui, then C# or VB6 all the way.
wait, does anyone even use VB6 anymore?