I just noticed on my mom's computer that some "MsMpEng.exe" process (labeled "Antimalware Service Executable" and located under "C Program Files\Microsoft Security Client\") is consuming 100% of CPU.

There are two common factors that can cause Antimalware Service Executable to take up too much CPU resources, from its real time feature and Full scan feature. Real time protection Feature is ...

This is an undesirable program. This file has been identified as a program that is undesirable to have running on your computer. This consists of programs that are misleading, harmful, or undesirable.