Imported From: http://groups.google.com/group/in-portal-bugs/browse_thread/thread/e1231bea60aacbf9#
What is "CreatedBySystem" field in sections (which actually checks, that ThemeId != 0) and what's difference between it and IsSystem field. For now all pages, that are auto-created during theme scanning have IsSystem field set to 1 and ThemeId > 0. When user creates virtual page, then it's always has ThemeId = 0. Can't see the difference.
This is related to discussion about section protection against deletion, since if we can figure out why we need that IsSystem field, then we can use it to protect pages, not to invent one more yes/no type field.