The most recent edition of Regulation, a magazine published by the Cato Institute, includes an excellent article entitled "Against ISP Liability" [PDF] by Cato's own Jim Harper.
Jim's article responds to an earlier article by Professor Douglas Lichtman, "Holding Internet Service Providers Accountable" [PDF], in which Doug argues in favor of holding ISPs liable for "malicious computer code" (viruses, worms, and other malware) that propagates over the Internet. A lengthier version of his argument is available at SSRN.
In my view, Jim has the better of this argument, pointing out that putting ISPs on the hook will inexorably lead to the lock-down of the Internet, as ISPs rush to protect themselves, often at the expense of the privacy and freedoms of their subscribers:
"Lichtman's proposal would drive responsibility from the edge of the network toward the center. By forcing intelligence into the middle of the network, ISP liability would push the Internet from a wide-open network toward something far more sclerotic."
Whatever your views on the ultimate question, it's a stimulating exchange between two smart thinkers.