Vuze Inc., a California-based company that provides a popular file-sharing program, is giving its users a tool to help figure out if their Internet service provider is interfering with their traffic.The Associated Press last year confirmed user reports that Comcast Corp., the country's largest cable company, was secretly disrupting some file-sharing by its subscribers. The company has acknowledged to the practice and said it's necessary to curb traffic that would otherwise slow down Internet speeds for other subscribers.The "plug-in" Vuze made available as a free download last weekend looks for "reset packets," the tool Comcast uses to break off some connections with computers trying to download files from Comcast subscribers, Vuze said Wednesday.The plug-in works with Vuze's main application, Azureus, which is based on the BitTorrent file-sharing technology. If the user allows it, the plug-in will send data back to Vuze, which will collect information about ISPs that are interfering with their subscribers' traffic.Palo Alto-based Vuze said Azureus has been downloaded 20 million times, and an average of 1.3 million users are using at any one time.Many U.S. ISPs — and cable companies in particular — acknowledge they are managing traffic. But most apparently apply more subtle methods that would not be identified by the Vuze plug-in.The Federal Communications Commission is investigating Comcast's methods. Also, the nonprofit People for Internet Responsibility has formed a Network Neutrality Squad to develop software tools that it will distribute for free to people who want to test what their ISP is doing.BitTorrent technology is used by several other programs. BitTorrent and eDonkey are the most commonly used file-sharing networks, and make up about a third of all Internet traffic, according an analysis by traffic-management and security company Arbor Networks last year.