Its probably a scam.. don't download it. It most likely replaces your login window with a fake one that steals your info.
Hack as in cheat for a game or as in cafe launcher that actually let you play all the games on all the VAC2 servers?
I bet it was one of these:
Outdated steam cafe launcher
Outdated key generator
Or something else outdated..
The security is much stronger, I don't think old programs would bypass it.
If you found a working hack.. why are you posting this..