Newbie questions regardsing negative hits

[Sylvan Andrew]

Hi,    I couldn't really find a clear answer about this one. Could somebody please give me some advice ?   I am using AmavisD with Spamassassin and it's being running great ! All of my users are happy campers. Suddenly overnight and I meen overnight my hits are negatives  like hits= -3.5  -4.3  -6.6  I am assuming this isn't a good thing. Could anybody please give me some info or advice as to what is happening ? Thanks heaps !   Kind Regards   Sylvan