[Chris M]

The owner/admin of any forum should not (and in most cases cannot) be held accountable for any content posted by someone other than themselves; To do so would be unreasonable...

Since the person who posted neither owns nor administrates/moderates your website, they have no say in how it is run; Therefore if you choose to edit/delete posts at random, that is your choice, not theirs...

The "line" is rather invisible; If you believe you are doing right by your forum, and not giving away personal data to third parties, as far as I am concerned that is within your rights as the owner/admin of the board. If you start to divulge personal information, then you could face legal action if the person can prove that you did this intentionally, or that the information is of a sensitive nature, or the data is gathered by your site/forum and has then been re-distributed therefore violating privacy... (Again, it depends on how your site is run)

The simplest way, is to write Terms and Conditions of use, outlining what you will and can do on your own forum, and that by joining the forum, all users accept any legal or civil actions taken against them and that you and your staff are in no way responsible for the actions of others, that you and your staff have the right to edit/delete content and anything else that you could possibly want to protect yourself from...

Chris