I asked this a while back, this I got from jstorms@livingston.com:
> From what I've been able to gather, the problem with the win95 'tracert'
> program is that it uses ICMP packets instead of UDP packets. The idea
> behind traceroute is to send out a series of packets (UDP packets) with a
> particular destination address. Each UDP increments the TTL (time to live)
> by one. Then as the packet is forwarded from hop to hop the TTL is
> decremented. When the TTL reaches zero an icmp time exceeded message is
> generated and sent back to the originator which is where all the hops and
> interesting data comes from. The problem is generating icmp time exceeded
> messages for icmp packets (as used by microsoft's tracert) with a ttl of
> zero is not a good idea (all kinds of terrible things can potentially happen).
So, yes, it is yet another micro$oft "feature" :-(
--Steven.