What's the User-Agent showing? Googlebot works according to it's specifications. If it's a bot, the user agent will be one of these:
Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)
Googlebot/2.1 (+http://www.googlebot.com/bot.html)
Googlebot/2.1 (+http://www.google.com/bot.html)
The bot ALWAYS identifies itself and must obey robots.txt