First off, that's not the orb's fault. Denethor's Palantir was hacked by Sauron. If a Maia wants to hack your wizardry equipment, then they're going to get in, orb or not. Any threat model that tries to defend from the fucking Dark Lord himself is completely bonkers. The only way to protect yourself from threat actors with that much power is to not make yourself interesting enough to be worth their time (see the Blue Wizards).

Second, Denethor wasn't even a wizard. If he was, he may have been able to recognize Sauron's influence and avoid pondering. But again, it's ridiculous to think you can defend yourself from those kind of threats.