I'll be the first to admit that computers? electronics? Not my thing. Technology is no friend of mine. Go look to my personal blog to see the swath I've cut through the ranks of electrical devices. If not for my internet addiction, I would probably be a Luddite.
So how can someone post to your account(s) without your permission?
- Well, the most obvious answer as to why there are things on your account that you didn't put there is that they hacked it. It's the answer most people leap to when they can see the posts and comments in question. I'd even be willing to bet it's sometimes true.
- Unfortunately, the internet is not the only thing that can be hacked. While it is true that proxies may physically haunt a person and physically hack into their accounts, the bigger danger is when they get into your head and use your own body to skulk about. Once you are "possessed" in such a way, I don't imagine it would be difficult at all for your secret-creeper to keep you from seeing things from the inside out, especially if you don't even know the information exists.
- The third possibility is that some kind of glamour has been placed on the blog/vlog to stop you from seeing the posts. The third seems unlikely simply because it would require a lot of work and fine tuning to make it apply only to one person. The internet not being a physical place, it would be very difficult (though not impossible) to do this... It's not something I'd like to try, but I do have theories on how it could be done.
A glamour would be difficult for a number of reasons. I don't know enough about computers to pull it off, but someone who's well versed in them AND in magic might be able to do it. That is part of the problem right there. While there are some people who like to refer to themselves as Techno-magi, I doubt the field is quite so advanced as this concept would require. Again, not an expert in this area, however Most of Slendy's followers just don't seem that bright.
Theoretically you would need the IP address of the devices(s) you wanted to affect in this manner, and possibly personal information and property from the human target as well. Though in this instance, information would be the better acquisition, considering this is a manipulation of information on the "information super highway."
While it is conceivable that all this information could be reduced to a sigil, a better solution would be to come up with a symbol to lock the specified target out, and then collect every single little thing that you wanted to keep from them as it was posted. I'm sure you can see how this could eventually become cumbersome. Again, not saying it couldn't be done, but it would be time consuming and tedious. The alternative, that you might modify the sigil each time some new thing was added would be even worse.
(This is for you Rev.) The simplest method for setting such a spell in motion would be to set up a website, put the lock sigil on the front page and make it the only thing accessible to casual observation. Upload everything you want to keep from the target and keep it inaccessible behind the lock sigil. Then just keep adding to the files as need be while posting them publicly to your hearts content. So long as the site hosting this spell never went down, the information would always be safe from the specified parties.