Protocols based on TCP, rather than UDP, are just as vulnerable. It is possible to hijack non-authenticated TCP connections, although it is somewhat more complicated. Attacks based on spoofing traffic coming from the distribution site of popular software packages is also possible. Berkeley, for example, is a mirror site for the Netscape browser. Any student with promiscuous network access on a machine between the ftp server and the main link to the larger Internet could have installed similar patching software to patch the huge number of copies of the binary that were retrieved from server.berkeley.edu.
More mundane attacks based on trojan horses or viruses remain viable today.
These attacks must exploit some other weakness in a system's security to infiltrate, but once in place they can perform patches to local binaries to fully compromise a system. Thus, unlike traditional viruses, the new strains will aim to have no visible effect on the system, thus making them difficult to detect and easy to spread unintentionally. Our patch of Netscape has this flavor. Fortunately, in practice it should suffice to handle far less than all of these risks. We hope to have demonstrated one gaping hole in practical security today, and to have highlighted the problem of the trusted endpoint.