I was getting some annoying 'messenger service' popups, and read in the
newsgroups that installing a firewall is a much better option rather
than disabling messenger service. I installed the sygate free firewall.
After installing this firewall, I started to get a lot of
sygate-generated popups, such as
"An application named NDIS User mode I/O Driver (file name ndisuio.sys)
has been blocked from accessing the network"
and
"IP network address translator (ipnat.sys) is trying to broadcast to
[239.255.255.250] using remote port 1900 (SSDP..........Allow...?"

Now I have no idea whether to allow these processes or not when asked
by the popup message. I don't know which process is authentic and
should be allowed, and which not.

Any suggestions?