When I wrote the previous post, I was unaware that my computer's firewall was off, and that it might be required. It turns out that the firewall is off by default because Linux is supposedly so secure that it doesn't need one. However, this might not apply to flash-drive installations, such as the one I use for most of my online activity. So, the problems I was noticing might have been caused by rogue hackers, or it could have been caused by the "NSA" (i.e. organized Satanism in the form of NSA black ops which answer to nobody, or at least no people) posing as rogue hackers.
So, I turned the firewall on (by entering "sudo ufw enable" on the command line, where ufw refers to Uncomplicated Firewall, an interface to the actual firewall), and I'll see if the problems persist. Even if they don't, I'll assume that the "NSA" can still snoop undetected at will, and that the only thing preventing them from doing anything noticeable is the fact that they could no longer pose as rogue hackers.