Rule writing - spamassassin-3.2.5-1

[Tom Brown]

Hi

I am getting loads of spam about various topics but a common theme is 
the URL within the message and that is

http://X7zfqxF7.spaces.live.com/

Does anyone know how i can write a rule to eliminate these?

spamassassin-3.2.5-1.el4.rf

thanks