PACKets that turn up unexpectedly on the wrong network because of bogus routing entries. Also a pACKet which has an altogether bogus (non-registered or ill-formed) {internet address}, such as the test loopbACK interface [127.0.0.1]. Such a pACKet will come bACK labelled with a source address that is clearly not of this earth. "The domain server is getting lots of pACKets from Mars. Does that gateway have a martian filter?" [Jargon File]