What, specifically, is a violation of due process? According to the story, ICE mistakenly included mooo.com in the domains they were seizing. Since that site functions as a DNS provider, the 84,000 subdomains hanging off it had their names resolved to the IP address with the scary law enforcement warning. That's a bad thing, of course, and I'll come back to that aspect of it - but it's not a violation of due process.
Let's back up a little. There are sites that host child porn or support a traffic in counterfeit goods, and part of ICE's job is to shut that down. Every country has a customs service, and the US is no exception. Art. 1 sec. 8 of the Constitution begins 'The congress shall have power to lay and collect Taxes, Duties, Imposts and Excises, to pay the debts and provide for the common Defence and general Welfare of the United States [...]' and later in that same section, 'to regulate Commerce with foreign Nations, and among the several States [...]' A1S8 is also the source of authority to act against counterfeiters (of currency), to define and act against piracy, and various 'Offenses against the law of nations.'
So there's nothing unconstitutional about the existence of an agency such as ICE: Immigration and Customs Enforcement are among the specific enumerated powers granted to Congress, and Congress can in turn delegate those powers to agencies that it creates. This is why some kinds of customs activities can be conducted without reference to the judicial branch - no warrant is necessary for inspection of cargo at the border for collection of customs duties, and the various other enumerated powers in that section combine to give the government fairly wide latitude to poke around in people's baggage and so on too. It should go without saying, but I'll say it anyway, that all nations assert the power to decide what may be imported, whether to protect their domestic agriculture or to prevent the spread of things like child pornography. Of course such power can be abused to support despotism too, but that's an issue of governance, rather than some inherent flaw in the law itself - just as a computer and the software it runs can be used for worthwhile or nefarious purposes.
Now when it comes to seizure of websites, ICE is exercising its power (as delegated) to regulate commerce, both foreign and interstate. For this, they do need to get a warrant. Here's an example of a warrant in template form: http://www.uscourts.gov/uscourts/FormsAndFees/Forms/AO109.pd... I am not sure if this the same warrant that would be used for a domain name seizure (IANAL) but if not then it will be quite similar - the principle is basically the same as impounding a boat or cargo container. Child porn is certainly subject to forfeiture, and if it's being trafficked across state or national borders, then all ICE has to do is show the court the website, the fact of its illegal content, and request the warrant be issued. And that's exactly what they do - there's no fourth amendment violation.
As for due process, that isn't abridged either in this situation. If the warrant was correctly issued, then the court is already satisfied that contraband exists. When it's executed against the listed websites, their domain names are seized and fall into the custody of ICE who has them redirected to their warning page. If one of the domain owners disagrees - say, because he does host porn but had a statement on the website that all performers are over 18 and he has documentary evidence on file - there is an opportunity to argue that in court. The warrant is not the end of the process; the government puts the seized property into evidence and a civil trial is held; if the government wins, then the domains become the legal property of the government.
Often in customs enforcement, counterfeit goods or money are seized but nobody is caught. The trial is still held; if you look at court calendars you'll see entries in federal district court every week for cases with names like 'United States v. $250,000 in cash,' or 'United States v. 100,000 capsules of a controlled substance,' or 'United States v. 5603 counterfeit handbags.' The US attorney describes the issue of the warrant and the seizure, displays the seized material or documentary proof of where it is stored, nobody shows up to contest the government's claim upon it, and the government wins and takes ownership of it (if it's money) or destroys it (if it's drugs or counterfeit stuff). I always like to imagine an actual heap of cash piled up on the defense table with its own lawyer in cases like these, but that doesn't happen :) Anyway, they will do the same thing as regards these seized domains that had child porn, and likely nobody will show up to claim them as their property - because unless they had ironclad proof that it was not child porn and so a legal mistake has resulted, then they'd be arrested for the criminal act of trafficking in such material.
With mooo.com, ICE made a technical mistake - but they made this mistake while they were in the process of executing a legitimate warrant. they have not any point claimed that mooo.com or any of its subdomains were involved in illegal activity. If they did so, then it would be weeks or months before the matter was put to trial. That the mistake was reversed within hours tells you that mooo.com was never listed on the search warrant in the first place. I'd bet money that the mistake actually occurred at a computer console - as the seized domains listed in the warrant had their DNS altered, the operator miscounted and pasted the ICE IP address over the next entry in the list, which happened to be mooo.com. Why? Because I have made that sort of mistake many times, and so has anyone else who uses a computer.
It is not acceptable, but it is understandable - whereas there is no evidence at all for the picture that's being painted of corrupt authoritarians abusing the helpless public. Imagine the scene: a technician sitting at a console, while some uniformed ICE officers clutching a crumpled warrant in their sweaty hands stand behind her, drunk with power. The technician says 'well, all done officers.' 'Wait! Wait! What is that other site, that m-o-o-o dot com?' 'Oh, that's just the next entry in the DNS database, officer - totally unrelated.' 'Well, I'm on a roll - take that one out too.' 'but, officer, that's not-' 'Silence! Obey, unless you wish to live out your life in a federal prison surrounded by the scum of humanity! I can totally do that, you know. Now, zap it!'
Really? You find that more plausible than a simple screwup, of the kind we have all experienced and which was quickly corrected? Come on.
I repeat, it should not have happened. ICE has a responsibility to use its enforcement powers carefully and accurately, and failed to do so here. Because mooo.com happened to be a DNS business, ICE's mistake did not just affect one site but mooo.com's 84,000 customers as well. And their mistake didn't simply result in those sites being inaccessible for a few hours - they resulted in those sites (and by implication, their owners and operators) being publicly identified as traffickers in child pornography.
That is a very serious charge, easily enough to wreck a person's reputation or even put their life in danger. When the government says such a thing about a person, even as a mistake which is quickly corrected, many people think no more but accord that accusation the same weight as a criminal conviction. With so many people affected, it's probable that at least a few of them have already been fired from their jobs, or received a visit from their local child protection services, or had their spouse file divorce papers. All those results would be radical overreactions to the sight of ICE's web page, but an official government seal and the words 'child porn' will be enough to provoke that in some viewers - it's literally something that people do not like to think about, and so people do not bother to question the immediate emotional response they feel. 10 years ago in the UK, a bunch of uneducated vigilantes ran a doctor out of her home - they misunderstood her job title of 'paediatrician' on her clinic door to mean 'paedophile,' assumed she was a sex offender, and vandalized her house. Imagine how much more damning an official government warning of actual crime must look to anyone unfamiliar with the DNS or the legal system. You'd be better off being accused of murder than a sex crime; even if you were falsely convicted, you would be able to survive in prison while you appealed. Convicted child abusers usually have to be isolated for their own safety inside prison, and are marked for life outside.
ICE's carelessness seems seriously negligent, and since so many people were affected a class action lawsuit against the agency seems very probable. Suing the government is more complex than suing a private party because the government has immunity from some kinds of liability, so I do not know what technical path the lawsuit might take. But for the government to slap a 'child porn warning' on 84,000 or more people at once, even if it was 'only for a few hours, and only on the internet,' is about as bad a screwup as you can make. With 1, 5, or 10 people it might be feasible for ICE to write some humble letters of apology and offer a settlement to mitigate their trouble, but with tens of thousands a trial is the only efficient solution.
But this was not a failure of due process - it's just another example of internet's multiplier effect. In this case, technology allowed a technical error to affect 84,000 websites at once. The problem here is not the law, but the fragility of the domain name system.