tl;dr:
Games affected:
- Fistful of Frags
- Team Fortress 2 Classic
- Fortress Forever
- No More Room in Hell
- Vikings and Knights 2
- Possibly other Source 2013 mods.
Games believed to be unaffected:
- Team Fortress 2
- Counter Strike: Global Offensive
- Dota 2
- Garry's Mod
- Counter Strike: Source
Workaround:
- cl_allow download 0
- cl_allowupload 0
- cl_customsounds 0
- Disable sprays