snort decoder WARNING: TCP Data Offset is less than 5

["Peter Van Eeckhoutte" <peter.ve () telenet be>]

Hi all,
 
I'm running a portscan against my boxes (nmap, with the fragmentation flag
enabled); and I'm getting a lot (thousands and thousands) of Snort alerts :
WARNING: TCP Data Offset is less than 5
 
This event doesn''t seem to be rule triggered, so I'd like to know how I can
turn off this event
 
Any suggestions/help is greatly appreciated
 
P