Flashed xbox 360s
 

I searched the forums, didn't find anything that is recent. Google isn't helping.

My brother is thinking of flashing his xbox 360. How likely is he to get banned from live?

very likely if he uses live with it.

I found quite a few message board threads on the subject using Google, what did you search for?

General consensus seems to be that using any flashed games on Live will get you banned pretty quickly. There are claims of patched games that you can use but I couldn't actually find any patches.

Not only will using copied games get you banned, but I've read that XBL can even detect the existence of the mod. If you're going to do it, have a second console to use on Live, and don't transfer or share anything between them.

The old practice was banning the console, not the associated gamertag. That may have changed recently though, I not 100% certain.