After 24 hours of observations, seems that I've found a final solution to the
last spam
attacks to my blog via trackbacks (I hope... 
). My last SQL Trigger seems
working good and during the last 24 hours I've not received trackbacks
spamming.
I don't want to post here the final solution (due to security reasons, I
don't want to give an advantage to spammers 
) but (obviously) if someone is
interested and will suffer of these types of spam attacks I will
be pleased to share the solution. However, the key seems to be checking the
blog_content table for Post Type = 3 or Post
Type = 4 (comment or trackbacks) and take actions consequently (basically a
filter based on my spam table).
How much this solution will resist to attacks? We'll see what
happens...