How do you protect your private information online? Someone posted my home address on the internet and it is not funny.
It is libel not slander - slander is spoken, libel is writen. Depending on what your doing and where you are then you most likely cannot protect your address online. Certainly in the UK your address is public record and whilst there are things you can do to limit the places where it can be obtained - make your telephone number ex-directory, ensure domains are registered to your business address or for personal websites that the whois is masked etc. The title of your post and the question however dont match.
There really isn't much you can do if someone posts your address online, unless you're a minor. For instance, you can easily find the address of a domain owner using WHOIS. If you own any domain names and didn't sign up for the special identity protection offered for an extra fee, then that is probably how others got a hold of your address. The only way you could get it taken down would be if the poster was threatening to harm you or slandering you.
Your home address was probably always published on at least a few pages on the internet (whois, switchboard, etc) Some domain registrars will offer a Whois privacy protection but I have not used that. I would rather want the domain name to be in my name and see that it is in my name. If you are worried about your address, you can rent a mailbox from a place like Mailboxes etc.