I guess I'm paranoid, but if they somehow get into your cyberware - wireless, microdrone, nanites, Van Eck phreaking, whatever - they can actually shut you out of your own DNI.
Most of my character's 'ware and gear has a reason to be connected to your PAN...for many of the same reasons that most of these devices have wireless (which I immediately disable, with wirecutters if necessary).
If you slave it all to your offline PAN hub, they have to hack that, which (unless you're a n00b) should be much more hardened as a target than just your basic limb.
Random thought. If a Technomancer physically touches your cybernetic limb, can they hack it? I'm low on coffee and can't remember the interface requirements for a Techno (never played one, personally - I can't do Emo.

).
-Jn-
Ifriti Sophist