Welcome to the joys of a closed ecosystem!
I find it a little incredulous that hacking would be SO prevalent that 3 lobbies in a row would be hacked games. Taking the post at face value, if I was guessing I'd say whatever hack the first lobby used was carried over to anyone that joined it, and when they joined a new lobby they inadvertently transferred the hack with them?
If that sounds far fetched, it's really not. Anyone that plays TF2 on Steam should have noticed that when joining a VAC secured, but modded server, sometimes the mods are not unloaded when the player joins a different server. It can result in all sorts of odd glitches or a crash when it happens.
There's also precedent with consoles, a la http://arstechnica.com/security/2012/10 ... ge-attack/
where poor game programming was to blame.... could just be the same with Ghosts.