"Undefined" basically means that the safety checker has not determined whether the web page is safe or not, so it is undefined. It should not be getting into your server logs but it does sometimes. This is why I refer to it as an error.
I see it in my server logs occasionally as well. Instead of returning a 404 and stopping the user from accessing the web page, I eventually put up a redirect (see my above post msg:4480395)
This is nothing to worry about. You are not being hacked or scraped. Eventually Chrome will correct this (maybe.)