Double Parity

When the phone booted it started up a command shell as root and sent every keystroke you ever typed on the keyboard from then on to that shell. Thus every word you typed, in addition to going to the foreground application would be silently and invisibly interpreted as a command and executed with superuser privileges.

Comical and apparently trivial to fix once identified, but still completely shocking that this kind of bug made it through three QA departments (Google, HTC and T-Mobile).