>you could just extend your argument to say that exploiting vulnerabilities in the user's browser to install tracking code directly into the binary is acceptabl

>you could just extend your argument to say that exploiting vulnerabilities in the user's browser to install tracking code directly into the binary is acceptable as well. Are you okay with that logical conclusion? No. That's not the logical conclusion; it's the extremist conclusion. The difference is that with things like cookies and ETags, the browser is designed to return that information back to the server. The server is not engaging in any malicious injection of foreign binaries or hijacking of program behavior. It's not doing anything to break outside of its allowed permission sandbox. It's using intentional, supported functionality in a non-disruptive manner. The only thing is that some people don't like that some of that functionality allows them to ascertain a user's identity after the user has cleared his/her cookies (ignoring here that the much larger privacy concern is the nearly-constant IP address of the user's home internet connection). If that's the complaint, and in this case, it is, then there is no fault from the server. The user should ensure that his/her browser is making those privacy controls available. Ignoring the problem and shaming companies for making the connection misplaces blame and allows the problem to remain, exploited only by those whose intent may actually be malicious. Obviously, there are many malware vendors who use their software to track users. I'm not defending them, nor am I defending those who exploit security bugs to get at data that they're not supposed to be able to access. That's not the case now; all of the fingerprinting methods discussed up to this point are fairly simple and do not involve coaxing software into any bad or illegal behavior, nor do they involve executing any spyware on the client machine. >It actually is how much of the world works. What ends up happening is people with no regard for ethics keep abusing this until regulations get passed to force people to stop doing things they know people don't want. No, it's not as simple as something "people don't want". Ethics are not about wants and conveniences, they're about behaving in a fair and honorable way. That's not the same as, and in fact it's sometimes the opposite of, what a customer may demand. Companies have obligations to non-customers as well. Today, customers are demanding that web publishers make all of their content available at no cost and with no ads. If we take the attitude that "if you don't want users to strip out your ads with client-side software, don't publish it online", it's just as fair to say "if you don't want companies to correlate your visits with server-side software, don't leak information that allows them to do so". If there's beef to be had with anyone here, it's the browser manufacturers who can't seem to figure out a way to engage in a normal conversation with a peer without leaking data that can be used to uniquely identify the user on the server-side.