I've got the details of a user who, amidst making useful edits, has committed 15 acts of vandlism over a period of two weeks. I have every reason to believe that if the user knows I am thinking of going public with that info he will attack my articles.
The best thing to do is list the person on the "vandalism in progress" page at http://en.wikipedia.org/wiki/Wikipedia:Vandalism_in_progress.
If you would rather remain anonymous, you could try emailing another user that you trust to make the report for you. There is a list of administrators at http://en.wikipedia.org/wiki/Wikipedia:List_of_administrators, many of whom you can email using the "email this user" feature on their user page. I'm sure that any of them would be happy to look into the situation for you without revealing your name to the vandal.
Angela.
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