1. An apparatus for verifying an identity of at least one user to a text-based communication with at least a second user, comprising: a memory; and at least one hardware device, coupled to the memory, operative to: obtain a plurality of pair-wise characteristic features of at least one prior pair-wise text-based communication between said at least one user and said same second user; compare the plurality of obtained pair-wise characteristic features to corresponding pair-wise features of a current session of said pair-wise text-based communication between said at least one user and said same second user; and verify said identity of said at least one user based on a result of said comparison.
3. The apparatus of claim 1 , wherein the plurality of pair-wise characteristic features are compared to a said current session using the statistical properties of the dynamics of user keystrokes.