[Ham-Computers] Protocol question (ICMP)

[WA5CAB at cs.com]

Can someone please tell me what an ICMP protocol is, what it's used for and 
what programs or type of programs might use it?  I'm getting both inbound and 
outbound hits that NIS is blocking (or stopping and I have to hit the confirm 
button).  Doesn't do any good to click the Always button as the IP addresses 
keep changing.  The inbound ones are one matter but the outbound ones have me 
wondering what's on my machine that wants out.  Neither NAV nor SpyKiller are 
finding anything.

Robert Downs - Houston
<http://www.wa5cab.com> (Web Store)
<wa5cab at cs.com> (Primary email)
<wa5cab at houston.rr.com> (Backup email)