Alan Paller makes a great point in a comment in today’s issue of SANS NewsBites:

Issuing a patch does NOT fix the problem. Vendor’s should not be allowed to get away with leaving major security flaws in software used in the critical national infrastructure without ensuring that (1) each buyer knows about the risk (emails haven’t changed, the right person is on the mailing list) and (2) the buyer has confirmed that he/she has the needed knowledge and support from the vendor to install the patch effectively.  As an  industry, we have to stop pretending that a patch release fixes a security flaw. Too often, a patch is never installed because the right person doesn’t know about it or know enough about it and no automated capability is in  place to ensure the patch is installed.

The general point, that a vendor issuing a patch does not mean that the problem is solved, applies far more broadly than just critical infrastructure. Microsoft has clearly recognized this, as they have created advertising and educational campaigns to encourage users to update old versions of Internet Explorer. For all the excitement that is generated when attacks against zero day vulnerabilities occur, most malicious activity on the Internet exploits software for which patches have been available for weeks, months, or years.