ur account wont get banned but ur xbox will - that means u wont be able to log onto live with that x360 ever again, no matter what
and ur console can get banned regardless of whether u actually play a pirate (or legit backup...) in the console or not
it also doenst matter if u havent been online with a pirated game or not - last round the firmware itself was detected, not the game itself (altho that was a secondary check, ex: playing a game well before its official release date)
so in conclusion, the theory for now with the latest firmware flash is that u can play online safely even with pirated copies (provided u dont play with ones weeks b4 the official release)
however that isnt for sure, and what microsoft do is gather data over a period and then ban tons of ppl at once, so no one knows the exact time or for what they were banned specifically
//edit also on the ban towards the end of last year they disabled harddrive functionality on the banned x360, this is no longer the case, and the latest dash infact restores the ability to install games to the harddrive even tho u have a banned console;