McCarthy revealed that a media law firm is being brought in to educate members of his squad about what they can tweet without incurring his wrath.
He will not bring in a blanket ban, but has not forgotten losing out on signing midfielder Steve Sidwell from Aston Villa last season after his interest was tweeted by an unnamed player.
McCarthy has now been linked with a move for former West Ham midfielder Thomas Hitzlsperger and that prompted Monday's warning.
He said: "Transfer targets of any sort, I wouldn't discuss them. I think what really should highlight that is we had Steve Sidwell at the Chelsea game here last season.
"Some twit tweeted it and it became common knowledge. Steve is on the running machine here and having a fitness test the following day and his agent gets a call from Mark Hughes and he goes and signs for Fulham.
"Now do you think that had anything to do with the grapevine or that Twitter line? I think it probably did."
McCarthy added: "Players are going to get themselves into trouble over Twitter, I can tell. I can't ban it and I'm not going to try. I've had that discussion today.
"You can't ban it. How can you? You try and make a rule like that and it just doesn't work. But they have to be careful what they say on it though, about the club and its policies.
"If they put a team selection up, which I'm sure some disgruntled numpty will at some stage, they will be in trouble for it. I think they can get fined for discussing that sort of thing.
"It is forbidden and I think it's unforgivable anyway. We are in the process of educating them, having a media law firm coming in to speak to the players about it."
Wolves are still awaiting the results of midfielder Adlene Guedioura's visit to a specialist after an ankle problem.