I went through the article "How To See Who Logged Into a Computer and When" https://www.howtogeek.com/124313/how-to-see-who-logged-into-a-computer-and-when/ which I found great.
When I reviewed some of the log-ins most of them were me but there were a few called
"Security ID: NULL SID"
and "Security ID: ANONYMOUS LOGON".
What are these and should I be worried about them?