Kurt Falde, one of our Support Escalation Engineers, create this summary about the recent definition changes:
In the past month the AV definition team have released some much needed changes with regards to AV definition and how they are downloaded to WSUS servers during sync intervals. While the changes do not affect clients from a size perspective they do slightly affect which packages they will download and install during an update.
I’m not going to go into how it previously worked here but if you are interested read the previous 2 articles for some background info: http://blogs.technet.com/b/kfalde/archive/2009/02/09/understanding-fcs-definitions.aspx
Instead I’m going to try to detail out what a WSUS server currently downloads from MU on a monthly basis as well as the signature interval basis (every 8 hours).
Summarizing the sizes
Engine Binary Difference Files
Base Definition Difference Files
Total Approximate File Sizes
Signature Release Interval (Every 8 hours)
6.00 Mb (this is average)
I want to stress here none of these file sizes are definitive. Definition sizes in general for the base sets are always growing. The BDD sizes are usually fairly consistent as well as the engine file sizes.