OK, I just saw it. I tracked down the IP address and it was a Yahoo web crawler. I'm not sure what actions may be taken by guests that aren't listed, but it must have been doing one of those actions.
Hostname: b3090905.crawl.yahoo.net
IP Country: United States
IP Country Code: USA
IP Continent: North America
IP Region: California
Guessed City: Sunnyvale
IP Latitude: 37.4249
IP Longitude: -122.0074
Organization: YAHOO
ISP Provider: Yahoo!