It is in fact the same thing. The marked bills and the malware serve the very same purpose in each example. I go to a bank and rob it, I end up with marked bills. The FBI then, through all the information at their disposal, requests a warrant and it is granted. They find said bills in my possession and I am charged. Same situation but this time I go to a kiddi porn site and while there I pickup a bit of identification malware that reports back to the FBI markers that are then used to obtain a warrant. Said warrant is then used to raid my home or place of business or where ever and they find kiddi porn on my computer as well as the malware. I am charged with the crime and take my chances in court. It is very much the same thing. The fact that there are others that are outside of the jurisdiction of the FBI also being marked in this is not relevant. If the FBI chooses to forward the information to the proper authorities in the offenders country and they are able to then prosecute them then I still don't see your point as to this being a non constitutional search. No search happens until after the offender visits the site, is marked with the Malware, Identified, and then a warrant is obtained in a court from a judge.