Putty and SSH problem "Server refused to allocate pty"

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@henryjfry

Im also concerned that its could be a security issue. Before the recent reinstall there were logs which showed numerous failed login attempts from randoms ips, hundreds of them presumably some sort of bot or something and I wasnt worrying about it becuase it was as secure as I needed it to be.

Are you port forwarding port 22?? Because you 1000% should not be forwarding port 22 from the outside world. You should set up your router to either be passing a randomly picked, non-standard port from the WAN side to port 22 on your Pi on the LAN side, or simply change the SSH port on the Pi to a random, non-standard port and forward that.