Having been involved with wikipedia for only a few weeks, I have just had my first "personal" experience of vandalism, ie. someone deleted the bulk of an article I had written, leaving an unintelligible stub. Fortunately I have been able to pick up the original text and put it back. I know that there are set procedures for dealing with this, but I would like to ask: How often does this kind of thing happen? And can I assume that this is vandalism rather than a simple error (bearing in mind that the perpetrator doesn't have a proper ID?