Shares of Equifax (EFX) were sinking by some 3% in midday trading Thursday on reports that the credit-reporting agency might have been subject to another data breach.

EFX fell to as low as $106.60 from Wednesday's close at $110.50 after the Web site Ars Technica reported the breach. Equifax has taken one of its customer assistant web pages offline as its security team investigates the report.

"We are aware of the situation identified on the Equifax.com Web site in the credit-report assistance link," Equifax spokesman Wyatt Jefferies said. "Our IT and security teams are looking into this matter, and out of an abundance of caution have temporarily taken this page offline."

Last month, Equifax disclosed that a massive hack compromised highly sensitive information covering more than 145 million people. That helped drive EFX's stock price down by more than 20% year to date. 

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