Too bad for them that it's on the workshop and it's a public file, if they were to update it with a virus and cause issues to peoples computers; then it would also update it for their own community and give them the virus also. Not to mention this is illegal, against steams TOS and also as far as I'm certain pretty darn impossible to do, the only thing that a workshop file can include is Lua, models and materials; things like most text files and DLL's and other such that you'd put into a file to create a virus are not allowed to be uploaded into a workshop file.
Personally, I think they are just saying a crackload of shit; and if you need that content then it doesn't stop you from just extracting the addon and placing it onto a fileserver for others to download.
But sure, better safe than sorry I suppose.