Hi kosakattack --

This was new to me, so I poked around a bit online to see if I could find anything. At a best guess -- and if you've got any examples of this being used in the wild, I can take a better look -- this seems to be a joking synonym for 招生. Apparently at some point there was a typo or printer's error that resulted in 招生 ("to recruit[ing] students") coming out as 招牛 -- literally, "recruiting cows," but actually something more like "recruiting awesome supremo badasses" thanks to the dual life of the word 牛. So if this is turning up in posts about hacking, maybe it's got to do with someone trying to get a super-1337 crew together?

Disclaimer: I could be waaaaaay off here. Have you got a link to an example of what you're talking about?

Side note: "herding" would usually be 牧羊/牧牛.