From what I read in my Toyota vehicle manuals the security code is something you as the owner program into the radio. If the radio is second hand and it is working, I would suggest the security has not been programmed. If it's second hand then that's a whole new ballgame... If it was previously programmed you need the code, but if it's working, chances are it hasn't been programmed. I don't know if non Toyota radios work the same but i imagine they do. Also, if the 'key' light is lighted up when the car's locked then it's likely that security is on.
I also suggest that in this day and age, if someone breaks into your car it's not the radio they're after, it's more likely your car will not be where you left it
Hope this helps
My 2013 auto D4D DC SR5, prefilter, 3" exhaust and Chip with egt probe, stock SR5 rims with Toyo Open Country AT2 265/65R/17's