Prank phone calls related to recent break-ins?

[natecars () REAL-TIME COM (Nate Carlson)]

I got an interesting call from one of my clients today. He said that one
of his employees had received a call last night, _at home_, from someone
claiming to be the system administrator for a 'major isp'. The employee
did not get the name or a contact number. The guy claimed that the
employee's account (he did not specify where; but the employee does
not have a personal internet account, so it would have had to happen from
the work account) was being used to hack his servers, and that the FBI was
already investigating. I ssh'd into the server at the business site, and I
could not see any signs of intrusion.. eg, no logs out of the ordinary, no
open ports that shouldn't be open, no trojans in place of real programs,
etc. Because of the fact that the caller contacted the employee directly
instead of the administrator for the system, and the fact that the caller
did not reveal anything that he would not know about the network (not even
hostnames or ip addresses), I am guessing that this was a prank call.  My
question is simply if anyone has seen unusual calls such as this. Thanks!

--
Nate Carlson <carlson () real-time com>    | Phone : (612)943-8700
http://www.real-time.com                | Fax   : (612)943-8500