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.

And Google, the leading online advertiser, stated that it has begun using Internet tracking technology that enables it to more precisely follow Web-surfing behavior across affiliated sites.

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.