Logcheck warning: UDP packet from outside my network?

[Matthijs <vanaalten@hotmail.com>]

Since a few days, Logcheck sometimes e-mails me the following warning:

Jun  4 07:30:54 MyMail kernel: UDP: short packet: 24.5.180.234:10030
2167/119 to 192.168.1.2:10768

I'm not really interested in what these packets are for (I guess some
kind of worm/DoS related packets), but I'm more interested in the
source of the packets: 24.5.180.234 is *outside* my network.

This Linux machine is located behind a hardware router with build-in
SPI firewall (Linksys WRT54G, in case you're interested). It should
prevent unwanted packets to uninteresting ports to enter my network.
I've just double-checked the port-forwarding section and packets to
10768 or 10030 are definitely NOT forwarded.

Can anybody explain what is going on here?

Thanks,
-- 
Matthijs
vanaalten@hotmail.com