Michigan's attorney general said she will file suit against DoubleClick under that state's consumer laws. DoubleClick's consumer monitoring "is a secret cyber-wiretap," said Attorney General Jennifer M. Granholm. "The average consumer has no idea that they are being spied upon," she said, and that lack of warning constitutes "a deceitful practice under our consumer-protection act."

The probes come as privacy advocates have stepped up their criticism about DoubleClick's business practices. Last week, the Electronic Privacy Information Center (EPIC), a privacy advocacy group, filed a formal complaint with the FTC, accusing DoubleClick of unfair and deceptive trade practices and demanding an immediate investigation.

EPIC's complaint alleged that DoubleClick was unlawfully tracking the online activities of Internet users, combining their surfing records with detailed personal profiles contained in a national marketing database of a firm DoubleClick recently acquired. That practice, EPIC charged, ran counter to an earlier promise by DoubleClick that the information it collected on Internet users would remain anonymous.