Seemingly random files keep taking up memory.

I'm running Windows 7 on my current PC with Norton 360. Recently, I performed a Norton task that required restarting my PC. When I turned it back on, memory was being consumed heavily by a few specific files. These files were: conhost.exe, dllhost.exe, cmd.exe, and now msiexec.exe. Here's what happens, one of these starts using up memory, it lasts for a short bit, and then it goes away. It should be noted that there seem to be two of whatever file is causing problems. The issues always pop up under one of these names. I've tried stopping it in the task manager, but I don't have permission, (despite being the administrator).

My question is, what should I do to stop this from happening? Also, what was the likely origin of this?

EDIT: Apparently, TrustedInstaller is a user on my device now. This seems related.