To dispel the myth that Bing clicks its own adCenter ads; Bing webmaster posted that “team is aware of an issue shared by all search engines: paid advertising links on sites are, on occasion, crawled and indexed by search engines. Standard practice in the search industry is to scan web pages for the purpose of indexing and understanding the site’s content, and to determine which ads match best the destination site. Microsoft adCenter does not charge an advertiser for clicks generated by any known search engine bots, including our own. AdCenter uses a variety of techniques to remove bots, including Interactive Advertising Bureau’s (IAB) Spiders and Robots protocol. The IAB provides a list of known bots, and Microsoft bots are a part of that list. As a result, any activity generated by bots will not skew AdCenter data because it’ll be categorized as low quality in AdCenter Reports. You can view the Standard Quality and Low Quality data by accessing the AdCenter Reports tab.
More info: adCenter blog