This enables the user who receives a program over the net to determine with some certainty who created the program. In ActiveX, the user can use the signature information only to decide whether or not to allow the program to execute at all. Java, as embodied in the most recent Java Development Kit and a forthcoming version of Lotus Notes, will allow users to configure their systems to allow programs signed by different authors to have different degrees of access to the system. They offer less protection, however, against viruses and worms. Because replicating attacks tend to spread along existing channels of communication, the people you are most likely to receive viral programs from are roughly the same people you are most likely to have in your trust database.
Viruses tend to spread along established communication channels, in the normal course of business.
On the other hand, modern systems are making that sort of spread more and more likely. Cold mathematics says that our only possible response is to increase the death rate accordingly. This means detecting infected systems, and preventing them from continuing to spread the virus, very quickly. A monthly update cycle will be far from sufficient. Turnaround times of a week, or even a day, will not be enough to keep a network-aware virus in check.