Update (Mar.22):
Today, I’ve updated Apache from 2.4.32 to 2.4.33. Now, MSE says all files are clean. What was that alert? Really compromised or not? Anyway, I backed the MSE settings to the default.
This morning Microsoft Security Essentials suddenly told Apache files are Trojan:Win32/Critet.BS and quarantined them, so Apache stopped on my server PC whose OS is Windows7 HE SP1. Although I needed to recover the service immediately, I had to take my mother to a hospital. Therefore the service must have been unavailable for about an hour.