Facebook has many applications you might tempt to use. One such application is the application which claims to show how many visitor visiting to your profile. Control yourself from using these kind of application. Check on net before using any application or don't use them.
Even after controlling yourself from using spam and wrong Facebook applications, you still can be unsafe. Your friend may be using them. In Facebook or any social networking sites, we sometime allow few people to come and be there as online friend. In this case, we might be giving important information, we otherwise don't give. This post will tell you how to save yourself from this situation.
Go to Account → Privacy Preferences and follow the steps shown through images. Allow only that much access to applications used by your friends, whatever you view as fit for yourself.
Click on link "Edit your settings" under Apps and Websites:
And, here you can see each part of your data accessible through friends applications:
I have debarred status update from access by application accessed my Facebook friend.
Facebook open data very easily to outside world but it give access to control it. It first open up data without asking us anything and that is a bad policy.