Patent litigation has doubled since the 1990s, with almost 3,100 cases filed in 2004. Since patents cover basic processes, including data transfer and one-click transactions, the practice of 'patent trolling' has become a major concern in the manufacturing sector. As technology evolves, patents become more valuable. So-called 'patent trolls' obtain their revenues chiefly from licensing patents they own and suing firms they deem to have violated them. The threat of costly litigation prompts many companies to settle suits out of court. Business and legal experts believe the problems surrounding patents stem from the U.S. Patent and Trademark Office (PTO). As more patent applications are filed, and as fees for filings rise, the PTO has a reason to approve more applications. About one-third of patents make duplicate claims, however. While 'patent trolls' deserve their bad reputation, some more established companies are also attempting to protect or corner certain markets. Legislation introduced in Congress would cap awards for patent holders that do not actually make the products, but the legislation has stalled, facing strong opposition from pharmaceutical firms and software vendors. To protect themselves, manufacturers are advised to understand risk and to determine if their customers face any risk. Companies that focus on a single product or that have straightforward production processes may have less to worry about than others. Firms using off-the-shelf software may be protected more than those that develop proprietary or customized technology systems. It is also important to research existing patents before introducing new products.