(2020-10-23, 01:44 PM)Torque Wrote: Would making the client open source leave unmodified servers vulnerable to attacks and also make it easier to develop hacks for OpenMP?

If you have unlimited access even to closed source application, you can hack it, there are no exceptions for this rule.
However if you don't publish source code of your application, you just hide its vulnerabilities (and there is special term for it: https://en.wikipedia.org/wiki/Security_through_obscurity).