You will see that since you are only viewing a certain circle of people, your status updates while on that screen default to only being seen by that same circle of people.
Note that this behaviour can be overridden by your site admin, in which case your posts will be "public" (i.e., visible to the entire Internet) by default.
If you look at the Contact Edit page for any person, we will tell you whether or not they are members of an insecure network where you should exercise caution.
If you mistakenly created a message and wish to take it back, the best you can do is delete it.
We will send out a delete notification to everybody who received the message - and this should wipe out the message with the same speed as it was initially propagated.
In most cases, it will be completely wiped from the Internet - in under a minute.
The decentralised nature of Friendica (many websites exchanging information rather than one website which controls everything) has some implications with privacy as it relates to people on other sites.
There are things you should be aware of, so you can decide best how to interact privately.
Our developers are working on solutions to allow access to your friends - no matter what network they are on.
However we take privacy seriously and don't behave like some networks that __pretend__ your photos are private, but make them available to others without proof of identity.
Your profile and "wall" may also be visited by your friends from other networks, and you can block access to these by web visitors that Friendica doesn't know.
Be aware that this could include some of your friends on other networks.
Blocking your profile or entire Friendica site from unknown web visitors also has serious implications for communicating with GNU Social members.
These networks communicate with others via public protocols that are not authenticated.
In order to view your posts, these networks have to access them as an "unknown web visitor".
If we allowed this, it would mean anybody could in fact see your posts, and you've instructed Friendica not to allow this.
So be aware that the act of blocking your profile to unknown visitors also has the effect of blocking outbound communication with public networks (such as GNU Social) and feed readers such as Google Reader.