&gt; I think you&#x27;d be hard pressed to argue that you have a 4th amendment right not to have the government link your pseudonym to your real name.<p>I would argue that it shouldn&#x27;t be content-based. It isn&#x27;t a matter of whether the information they want is the human corresponding to that pseudonym, it&#x27;s a matter of whether you had a reasonable expectation of privacy in that information, which depends not on what the information is but on what you did to protect your privacy.<p>If you make a public statement under your pseudonym that identifies you then you don&#x27;t have a reasonable expectation of privacy in that information. But if you take reasonable steps not to link yourself to your pseudonym, why should the government be completely unrestricted in how it obtains that information without a warrant, no matter how underhandedly or unexpectedly they behave?<p>The alternative is essentially an unwarranted expansion of the third party doctrine: Instead of saying that if a third party <i>does</i> know something the government can get it, it&#x27;s saying the government can get anything a third party <i>could</i> know even if they wouldn&#x27;t normally be expected to observe or record it -- or even if they implicitly or explicitly agreed that they wouldn&#x27;t.