Strange UDP(137) connection attempts

[KissCool]

My firewall logs become stranger and stranger. I have had a lot of connections attempts for 2-3 weeks on my port 137 with UDP from several differents IPs. Obviously, there is always this sort of connection attempts on this port, usually 5 or 6 times each hours, but as you can view my logs of a little connection today, it's far more than usual things.
I have a simple dial-up connection, my port 137 is closed and I use strong rules for my firewall. I have some hypothesis but I want to hear your opinions about this. Thanks.

22/12/2002 15:54:45 Connection request 4.47.88.206 UDP(137)
22/12/2002 15:53:54 Connection request 200.44.115.74 UDP(137)
22/12/2002 15:52:12 Connection request 200.161.197.32 UDP(137)
22/12/2002 15:51:46 Connection request 62.139.144.195 UDP(137)
22/12/2002 15:51:26 Connection request 61.38.150.24 UDP(137)
22/12/2002 15:50:33 Connection request 219.167.6.87 UDP(137)
22/12/2002 15:50:00 Connection request 219.112.80.190 UDP(137)
22/12/2002 15:49:00 Connection request 81.50.88.169 UDP(137)
22/12/2002 15:48:40 Connection request 212.96.198.65 UDP(137)
22/12/2002 15:45:29 Connection request 218.162.109.195 UDP(137)
22/12/2002 15:45:09 Connection request 200.65.89.230 UDP(137)
22/12/2002 15:44:30 Connection request 219.118.18.50 UDP(137)
22/12/2002 15:39:44 Connection request 64.163.22.38 UDP(137)
22/12/2002 15:38:49 Connection request 61.220.40.10 UDP(137)
22/12/2002 15:35:39 Connection request 195.34.229.114 UDP(137)
22/12/2002 15:24:18 Connection request 210.66.61.104 UDP(137)