A recent NY Times article[1] talked about just this.  On auction sites like ebay, competitors can lock that accounts of those they're bidding against in order to win auctions.<p>1. <a href="http://www.nytimes.com/2010/01/21/technology/21password.html" rel="nofollow">http://www.nytimes.com/2010/01/21/technology/21password.html</a>