Possibly. You don't want to use the older client for anything except connecting to the older system. Keep it somewhere offline (encrypted, whatever: distinctly

Possibly. You don't want to use the older client for anything except connecting to the older system. Keep it somewhere offline (encrypted, whatever: distinctly non-executable), too. (Not that it would solve the issue altogether, see Stuxnet for a sufficiently motivated attacker and airgapped systems, but it's a viable mitigation.)