My friend asked me about a warning he got over the PC-Cillin firewall that said "ICMP echo requests".........and it pops up continuously to warn him... and he is asking me what it is......so.... i come to this home, and hope can get some answer out of it.....

Question
1. what is ICMP?
2. what's the threat for ICMP echo request... (comming from the NACHI.A virus)?

Thanx to the one who takes time to read my thread and response....