Q: Why is a process, mscorsvw.exe, using huge amounts of processor in my environment?
A: Don't worry, this isn't malware. It's the engine optimizing the .NET Framework on your machine.
If you install an update to your machine that includes .NET Framework updates, it's common after the patch is installed to see the mscorsvw.exe process using high processor amounts for a short period of time (minutes, typically).
By default, the process will use only a single core; however, if you have more cores available on the box, Microsoft has a script available in an MSDN blog post that allows up to six cores to be used and therefore the process finishes faster.