Amazon.com said it has filed suit against rival bookseller Barnesandnoble.com, saying it illegally copied a shopping feature on Amazon's site. The suit, filed late Thursday in US District Court in Seattle, alleges patent infringement and seeks an immediate and permanent court-ordered halt to the defendant's copycat feature. It also asks for an unspecified amount of damages, Amazon said. The suit centers on a feature called 1-Click, which was introduced in September 1997. The feature is designed to allow customers to shop without having to re-enter their shipping and billing information every time they buy. Amazon received a patent on 1-Click last month. In a statement, founder and CEO Jeff Bezos said: "Being a pioneer and innovating for customers is always hard. We spent thousands of hours to develop our 1-Click process, and the reason we have a patent system in this country is to encourage people to take these kinds of risks and make these kinds of investments for customers." Back in April, Amazon settled a legal fight with another competitor, retailing giant Wal-Mart Stores. Wal-Mart had sued Amazon, charging the company with stealing trade secrets by recruiting Wal-Mart employees and business partners in order to copy the discounter's massive computer system. Amazon had filed a countersuit in the same state court, deriding Wal-Mart's efforts to do business on the Internet and accusing the retailer of chilling its employees' ability to look for work elsewhere. The out-of-court settlement required Amazon to reassign at least one former Wal-Mart employee, limiting the job responsibilities of other former Wal-Mart employees, and requiring all former Wal-Mart employees to return any Wal-Mart property they still have.