This information was from a documentary on SETI and the search for Life, as it aired on Discovery channel. Carl Sagan also wrote about this procedure in Contact. Yes, yes I know it was a work of fiction, but the Author being Carl Sagan, it's relevant.

Here is a link that describes moving the telescope off target and getting independant verification:


here is a link for a paper that also may shed some light, although it deals more with proving the signal defies entropy and is not terrerstrial.

edited to add links.