A user of an internet search engine — Google, Bing, Yahoo! — who includes a well-known trademark in a search is likely to see a group of ads related to that mark. These ads — typically appearing above or beside search results — may identify dealers or suppliers of the trademarked product, link to sites that offer advice or product reviews or point to sellers of competitive goods.

None of this is an accident: Competitors of trademark owners, as well as the owners themselves, bid on the right to place sponsored links keyed to trademarks in favored positions on pages that display search results.