I don’t want to argue against you, but like the guys in your forum post already told you, it is a nearly zero percent chance that someone hacks into a pc, takes your BPs, changes them and puts them back into a different folder.
This is by far the most senseless explanation of this error. No one would hack a random person with the knowledge of changing Blueprints.
You said your Engine/Computer crashed when you tried to add something to your scene. This sounds more like your PC didn’t save the files properly and maybe put them into a Temp folder or something.
Most of us had errors in some kind of stages where Blueprint Nodes disconnected or the whole Engine didn’t want to open again, because we messed up a Blueprint. Everytime the Editor starts, it tries to compile the Blueprints as far as i know. And if you messed up a Blueprint and crashed your Editor it is way more likely that this broke your Blueprint.
If you want help, you need to tell the information he asked for. Engine Version etc. I think your Blueprint is just broken, because your Computer crashed. So a dxdiag would be nice too, to see if your PC has some trouble to handle the Engine at all.
Try to calm down and think what you may have done to cause this kind of crash. I don’t know if theres a crashlog that you could post. Maybe could tell where to find this, so he could see what did crash your Editor.
The only other thing i could think of is, that you downloaded a simple virus that moves random or last used files. After they got moved, you got reference errors inside your Blueprints, because they missed the moved files. This also leads to Nodes disconnecting.