Horizon Blue Cross Blue Shield of New Jersey says the password-protected, unencrypted laptop computers were stolen over the weekend of November 1st from its Newark, NJ headquarters.
The theft was reported to Newark Police on Monday November 4th.
The company says the computers may have contained files with clients' personal information, including names, addresses, dates of birth, and in some cases Social Security numbers.
The insurer said approximately 839,711 members were being notified as a precaution.
A company spokesman said in a statement that there has been no evidence of identity theft or other misuse of personal information, and that anyone whose Social Security numbers were compromised would be offered free credit monitoring and identity theft protection.
MORE INFORMATION: horizonblue.com