Updated Friday, Aug. 29 at 9:45 a.m. EST

The personal information of more than 12 million people was stored on an unencrypted Bank of New York Mellon backup tape that went missing earlier this year, the company said Thursday.

The tape initially was believed to contain data on 4.5 million people, but the number was revised after a forensic review that came in response to subpoenas issued by the Connecticut’s consumer protection commissioner, Jerry Farrell Jr.

“Obviously this raises a lot of questions for us,” Farrell told SCMagazineUS.com on Thursday. “Where was this other data? Where did it reside that you didn’t even [initially] realize it was on that computer tape?”

Ronald Sommer, a BNY Mellon spokesman, told SCMagazineUS.com that the bank plans to notify around eight million more people, bringing the total number of affected individuals to some 12 million.

“We fear a substantial number of Connecticut residents are among this latest group,” Rell said in a statement.

About a half million Nutmeg State residents initially were affected by the lost tape, which was reported in May but actually went missing several months earlier. Most of those were People’s United Bank customers. BNY Mellon was assisting People’s parent transition to a public company.

Data on the tape included names, Social Security numbers, addresses and birth dates.

A BNY statement on Thursday said the institution has no reason to believe any of the information has been misused. The bank plans to offer all affected individuals two years of free credit monitoring and $25,000 of identity theft insurance.

Since the breach, the bank said it is attempting to transfer data internally without the need for storage tapes, when technically possible.