WellPoint Inc., the largest U.S. health insurer, had no reports the information was misused, spokesman Jim Kappel said.
Most of the 196,000 affected people are Anthem members in Kentucky, Indiana, Ohio and Virginia, Kappel said.
The back-up tapes were stolen from a Massachusetts office of Concentra Preferred Systems, a company that audits and analyzes WellPoint's claims information, The Courier-Journal in Louisville, Ky., reported.
People whose information was stolen were notified in a recent company letter.
The theft occurred in early November but it took time to determine which members' data were on the tapes, Kappel said.
No arrests have been made, he said.
WellPoint was formed in late 2004 from the merger of Anthem and WellPoint Health Networks.
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