Moravec Operator

I'm studying a computer vision module at university and a Moravec filter for detecting "points of interest" was mentioned but I can't make sense of the details we were given.
Can anybody post or direct me towards an algorithm either in a programming language or pseudocode so I can see exactly how it works? An explanation would also be fine as long as it is concise.
I've looked around online but not come across anything which I am 100% sure about.

Thanks in advance for any helpful replies.