lets say, someone gave me an android phone ( with custom rom, lets say CM or etx). i did hard reset to erase alll data and usr apps. but i am interested, how to know if that custom rom is not modified ( if i am afraid of spyware hard-coded into that os).
how to check if that system is clean from such custom modification, and is an original CM?
EDIT: I've found interesting answer here - How to tell if phone's ROM is original or tampered?