Bundling of Microsoft Windows is the installation of Microsoft Windows in computers before their purchase. Microsoft encourages original equipment manufacturers (OEMs) of personal computers to include Windows licenses with their products, and agreements between Microsoft and OEMs have undergone antitrust scrutiny. Users opposed to the bundling of Microsoft Windows have sought refunds for Windows licenses, arguing that the Windows end-user license agreement entitles them to return unused Windows licenses for a cash refund. Although some customers have successfully obtained payments (in some cases after litigation or lengthy negotiations), others have been less successful.