Equifax shares sank to a 19-month low on Wednesday after the Massachusetts attorney general announced that she was preparing to sue the credit bureau over one of the biggest data breaches in history.

“In all of our years investigating data breaches, this may be the most brazen failure to protect consumer data we have ever seen,” Maura Healey said in a statement.

Already reeling after a disclosure last week that a May cyberattack may have stolen the personal data of as many as 143 million Americans, Equifax saw its shares fall nearly 15 percent on Wednesday, to $98.99.

Since the announcement of the cyberattack — which compromised Social Security numbers, driver’s license numbers, credit card numbers and addresses — Equifax shares have fallen more than 30 percent.

Massachusetts joins New York, Pennsylvania and Connecticut in investigating how Equifax got hacked.

Equifax, one of the three largest credit bureaus, stoked customer anger during the past six days in one bungled p.r. move after another.

First, the company waited months to alert the public after first discovering the breach on July 29. Three top executives sold almost $2 million in stock days later.

Then, after announcing the breach, Equifax demanded customers give up their right to sue the company in exchange for free credit-monitoring services — and then charged them to put a freeze on their credit. Both the fee and the demand have been rescinded.

Even though the breach is one of the largest ever, and may already be responsible for a spike in consumer fraud, Wall Street was surprised by the extent of the public’s anger.

“To be frank, I’m surprised this has stayed in the headlines this long,” Brett Horn, an analyst at Morningstar, told The Post. “To some extent, it’s because the company bungled the p.r. of this breach post-announcement.‘’