( anyone else notice the recurring 8 here? )

Although steve.milner obviously sees the same thing I do, I would not do what he suggested. I would walk away. Any client that would say such a thing will just bad mouth you to death each time he/she calls you back. In the long run it will be bad for business.

Since you ( h8spame ) didn't say what these machines are used for ( personal computers or small business with web server, etc. ) it is hard to really give advice except that you need to clean it all, then advise client on appropriate use ( put that in writing if necessary so there is no mistake ) and how to better secure the machines ( and you would do it at additional cost. )

( also see XTC46's post above ).
Additional questions in my mind,
What type router?
What capabilities of the router?
Again, is this a personal network or commercial network?