We automatically update one to many times a day the list of tens legitimate services among which:
Googlebot, Google crawlers, Msn, Facebook, Yahoo, Yandex, Linkedin, Exalead, Duckduckgo, Blekko, Baidu, Pinterest.
If you think a search engine or a website should/not be among this list, you may just add it into your GP Firewall ruleset and it will be instantly authorized/denied depending on your choice.