grrr. This headline is misleading and sensationalist; nothing in the linked article supports the assertion that the order is for all of the followers of @wikileaks. It's bad enough that the Government is subpoenaing the information of people who actually did things in cooperation with wikileaks (including a legislator from a foreign government), we don't need misleading and downright false headlines muddying the debate.
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EDIT:
OK, I had not seen the tweet from @wikileaks when I wrote the above.
I still think the headline is misleading. But that's up to you to decide.
It requests a considerable amount of information (name, phone number, email, IP, usage logs) for "each account registered to or associated with Wikileaks", including "connections made to or from the Account" and "correspondence and notes of records related to the account", which to me would at least imply anyone who has ever replied, retweeted, or DM-ed them.
I would also look at the incident at Columbia University in which students were warned not to discuss WikiLeaks on any social networking sites if they were planning on getting a public sector job. The subpoena is targeting just that sort of information.
Because incidents like this are so new, there is little legislation or precedent with which to weigh the matter. However, the government has shown that in most cases, a loose interpretation of the law is taken, and I would argue that they apply their powers as broadly as possible until otherwise told not to. Based on subpoena laws for emails and the string of DMCA subpoenas, in addition to the PATRIOT Act, the Supreme Court (which also currently has a conservative majority) would likely rule in favor of such a broad interpretation based on stare decisis.
In my opinion, Twitter wouldn't have pushed for the unsealing of the subpoena if they didn't think it affected a significant number of their users.
As far as why I posted it, it's an important issue that has widespread ramifications, especially for the Hacker News community. Although I personally feel strongly about the issue, I think even the possibility of a subpoena like this should be discussed regardless.
Update (12:20am GMT): Mark Stephens on the BBC News also makes clear that the court order will also cover the “600,000 odd followers that Wikileaks has on Twitter“.
If it really does, that's an overreach by the prosecutor and the judge should not grant the order.
But my reading of the order linked by Glenn Greenwald is that it is asking for information on the named twitter accounts, not the recipients of messages from those accounts.
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EDIT:
OK, I had not seen the tweet from @wikileaks when I wrote the above. I still think the headline is misleading. But that's up to you to decide.