Those who friends with you on Facebook have access to some of your data, as do the apps they use. You can restrict this to apps used by friends by tweaking certain security settings. Log into your Facebook account, click on "Settings" and select "Privacy Settings". You will see the "Apps" category to the left; click on it. Here you will find several options, but click on ‘Edit’ next to ‘Apps others use’. Here you will see all the information that can be accessed by apps your friends use. This includes information like your bio, birthday, status updates, photos, links, activities and much more. If the box next to any of these categories is checked, then it means that the information is available to that app. Uncheck the box if you do not wish to share this information and confirm with "Save changes".