General Mortgage Acceptance Corp. is GM's mortgage lending firm. It recently filed a lawsuit against online mortgage lending exchange LendingTree, for using the address gmac.realestate.com to promote its lending services. Obviously, this name was almost identical to GMAC's www.gmacrealestate.com.
But GMAC dropped its lawsuit when it realized that any word or combination of characters (and not just gmac) that is entered before .realestate.com (owned by Lending Tree) will divert users to this website.
This technique is also called "wildcard DNS". There have been other stories like GM's, reported in this article, footnote 17 (article in French but references in English).