It really depends on your social circle and what area of infosec you're in. I've socially been in the 'hacker community' for most of my life and virtually nobody that I associate with from there has an actual CS degree.

A few folks got Physics degrees, but the vast majority of people I know left school to work and have not finished. Myself included.

The other very common backgrounds that I encounter is people who served in the military and people who backdoored their way into it from being sysadmins.