Several Internet and broadband companies have acknowledged using targeted-advertising technology without explicitly informing customers, according to letters released yesterday by the House Energy and Commerce Committee. The revelations came in response to a bipartisan inquiry of how more than 30 Internet companies might have gathered data to target customers. Some privacy advocates and lawmakers said the disclosures help build a case for an overarching online-privacy law. Increasingly, there are no limits technologically as to what a company can do in terms of collecting information . . . and then selling it as a commodity to other providers," said committee member Edward J. Markey (D-Mass.). "Our responsibility is to make sure that we create a law that, regardless of the technology, includes a set of legal guarantees that consumers have with respect to their information." Markey said he and his colleagues plan to introduce legislation next year, a sort of online-privacy Bill of Rights, that would require that consumers must opt in to the tracking of their online behavior and the collection and sharing of their personal data. Ari Schwartz, vice president of the Center for Democracy and Technology, said lawmakers are beginning to understand the convergence across platforms. "People are starting to see: 'Oh, we have these different industries that are collecting the same types of information to profile individuals and the devices they use on the network," he said. "Internet. Cellphones. Cable. Any way you tap into the network, concerns are raised."