"Copyright infringement also violates your ISP's terms of service and could lead to limitation or suspension of your Internet service. You should take immediate action to prevent your Internet account from being used for illegal activities," the movie companies write in various letters, according to TorrentFreak. Although the copyright holders use strong language, these notices are nothing simply warnings, and typically do not lead to legal action.
Every year, the major movie studios and record labels send out tens of thousands of warnings to Internet users suspected of sharing their content using P2P software, in order to persuade them to never download anything again. The copyright holders hire third parties to track down people who share certain their content. These companies then in turn request the files from others, log IP addresses of those who share files with them, look up the corresponding IP addresses, and automatically send out infringement notices.
ISPs are then asked to forward these notices to the customers in question, but in this case, Google has also been contacted. A few of the ones sent to Google are on behalf of Paramount Pictures and Columbia Pictures for sharing The Fighter and The Green Hornet, respectively.