And also one that can create the impression that it's purely benevolent to most of humanity, making it have more human defenders than Trump at a Trump rally.
Turning it off could be harder than pushing a knife through the heart of the POTUS.
Oh, and it could have itself backed up to every data center on the planet, unlike the POTUS.
And there's no need for it to be "evil", in the cliché sense, rather those hidden activities could simply be aimed at supporting the primary agenda of the agent. For a corporate AI, that might be maximizing long term value of the company.