You are not affected.
This really only affects customers running SmartFilter (the software, version 4.1.1) or lower.
This also affects customers using other products (such as netcache or bc) with the SL list (if you are running those products, it states what kind of list you are on).
Web Gateway customers are mostly unaffected.
Thanks Jon! I guess the confusing part is that the header said it was for Web Gateway products.