Is it possible to determine whether the phone has been rooted or not? Let's say I buy an "un-rooted" Samsung Galaxy S2 via eBay that's still under warranty:


Is there a way I can tell whether it has been rooted before (with or without rooting it myself)?
Is there a way Samsung can tell me whether it has been rooted before?
Most Samsung Android phones and tablets can be restored back to "stock" firmware via Odin or Heimdal tools. This wipes all traces of rooting or any other kind of system alterations, and in most cases is sufficient for sending the device in for in-warranty servicing to the carrier of manufacturer. However, with the Galaxy S2 series of devices Samsung introduced a hidden "flash counter" which keeps track of how many times such a tool has been used.

A community developer actually found where this information is stored and created an app that allows you to reset the counter.  Unfortunately the app only works on ICS (Android 4.x) right now.  See this thread on XDA-Developers forum for more details.