Due to the physical separation of the conductors K&T is safe when left alone. What’s left of the insulation on most K&T will crumble at the slightest touch so crawling through the attic can be a dangerous adventure.
Homes with K&T usually have fewer devices per square foot than today and the K&T I have seen always has been installed in a very professional manner. So you are not likely to have a rats nest of it in the attic.
My house has K&T and I don't loose sleep over it. While if I found out I had aluminum I would be ripping out the walls tonight.
My main area of concern with K&T is where it enters J-Boxes, since this is where it looses the protection of physical separation. However there is no easy way to check the junction boxes without possibly making the situation worse. And if there is an issue, that’s what the j-box is there for, to provide protection.
