I recently found a good link which explains some of the details of copyrighting your work with a focus on online stuff.
'The problem with copyright on the internet lies in enforcement; the internet is so huge and so truly international that you probably won't ever know if someone has infringed your copyright. It can help to make a clear statement setting out the extent to which you are happy for others to use your material without permission.' (extract from the site)
Remember, always mark somewhere on your work it is copyrighted. There are ways you can prove you created something before somewhere else - dated files on your pc for example but it is always best to play safe.