That's only a very slight exaggeration. In theory if you found every server that was hosting a copy of something and removed it, you could get it off the internet. If it's something no one has any interest in it won't be hosted on as many servers. Something that's gone viral could easily have millions of copies. It's possible you could write a malicious script to track down every single copy and destroy it entirely, but it would have to be insanely advanced. Magic might make it easier, but that would depend on the magic.