Also, there are potential fire hazards with the break down of the insulation around the knob and tube wiring that comes with age, and should the black and white wires make contact.
The advice my family once got from an electrician on this question was that if you have low amperage service and NEVER touch it, you're probably okay.
Knob and tube wiring is usually found in homes built about 50 years ago that have not had the wiring updated.
All insurance companies view this wiring method as a serious safety hazard and most require an insurance inspection before a policy is issued.
It seems really old and brittle, so I'm a little concerned.
His basic theory was that if you keep the wires cool, and they haven't caused you trouble yet, it's unlikely to cause a problem.