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server not to cache that object. However, due to the misuse of the header by content providers, many proxy
cache administrators have resorted to ignoring the header and caching the resource anyway. Cache busting
methods include appending a random segment to the URL which confuses the cache into thinking that all the
resources are different, and generating all pages dynamically through a cgi-script, the results of which do not
get cached.
Working with the cache implies that you allow the proxy to cache your resources, and you are supplied with a
log of cache-served resources originating from your server. This is not feasible without some form of
automated system, as the number of proxy-cache servers is huge, and the structure of the proxies is completely
uncontrolled. Such systems are under development, and when ready, it may be in the proxy cache's best interest
to supply such information, as it might help the cache-busters in their defection from enemy to ally! To send
information about each request to the origin server of every resource in the cache would severely impact on
Internet bandwidth, and reduce the benefit of running a cache in the first place. It may be feasible however to
consider some form of periodic batched transfer of information to selected origin servers that requested the
information by setting a special header when the resource was first requested from the server.
It is worth taking a paragraph to consider the impact of proxy caches on the unavailable image and Java applet
solutions presented above. Based on experiments with NCSA httpd 1.5.1, proxies do not cache 404 unavailable
responses, which means that this solution will work to track users behind proxy caches and firewalls.
Furthermore, it will not impact on the network as much as cache busting algorithms, because no data is being
transferred - only the request for the unavailable image. Java applets are cached by the proxy, but they are still
allowed to communicate directly with the tracking server. There have been some problems with running
networked Java applets from within Netscape from behind firewalls. At the time of writing, the author knows
no solution to this particular problem.
This concludes our discussion of current and possible techniques for tracking users as they access the World
Wide Web. The following section now briefly discusses some of the ethical issues that arise as a result of this
idea.
Privacy and Ethical Considerations
Techniques for tracking users, as discussed in this paper, raise a number of ethical issues concerning privacy
and security. Such issues are complex and hardly ever clear cut. However, they are also of great importance
and so warrant discussion and consideration during the technical development process. We begin by
identifying the kinds of information that might be gathered about the presence and activity of users on the
WWW. These include:
• Monitoring general access trends - recording patterns of access by groups of people.
• Anonymous monitoring of individuals - recording details of an individual's access but ignoring their
identity.
• Non-anonymous monitoring of individuals - also recording the identities of people accessing the WWW.
• Persistent recording vs instantaneous awareness - deciding whether monitoring information is recorded for
subsequent storage, analysis and use or whether it is only made available at the time of access (e.g. to
enable chance encounters and stimulate social interaction).
There are may also be many possible uses of such information. For example:
• Making colleagues generally aware of each other's presence in much the same way the shared buildings
and offices support the coordination of activity through casual awareness between their occupants.
• Encouraging chance encounters between people browsing the same or related information.
• By information and service providers in order to enhance services (e.g. developing new paths through
information based on analysis of patterns of use) or as part of billing and accounting.
• To enhance security by providing better awareness of who is accessing which sites and information (in the
same way that video surveillance improves the security or many urban areas).
• It may be made available to third parties such as advertisers and government agencies.