If you look carefully when visiting a group from your Network page, the lock icon under the status update box has an exclamation mark next to it.
This is meant to draw attention to that lock.
Click the lock.
You will see that since you are only viewing a certain group of people, your status updates while on that screen default to only being seen by that same group of people.
This is how you keep your future employers from seeing what you write to your drinking buddies.
You can over-ride this setting, but this makes it easy to separate your conversations into different friend circles.
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.
But it isn't as clear cut when dealing with GNU Social and other network providers.
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.
Once you have created a post, you can not change the permissions assigned.
Within seconds it has been delivered to lots of people - and perhaps everybody it was addressed to.
If you mistakenly created a message and wish you could take it back, the best you can do is to 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 it was initially propagated.
In most cases it will be completely wiped from the Internet - in under a minute.
Again, this applies to Friendica networks.
Once a message spreads to other networks, it may not be removed quickly and in some cases it may not be removed at all.
In case you haven't yet figured this out, we are encouraging you to encourage your friends to use Friendica - because all these privacy features work much better within a privacy-aware network.
Many of the other social networks Friendica can connect to have no privacy controls.
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 sitefrom 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.