Hackers were moving freely in Equifax Inc.'s (EFX) - Get Equifax Inc. Report computer network for months before the company discovered a breach, the Wall Street Journal reported citing a confidential note Equifax sent to some of its customers. 

Cybersecurity firm FireEye Inc. (FEYE) - Get FireEye, Inc. Report , who was hired by Equifax to investigate the breach, discovered the extent of the hack. 

Hackers infiltrated the company's system in March, not May as had been originally reported, and Equifax did not discover the breach until July 29. The company announced that it had been hacked on September 7. 

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Equifax shares have taken a beating since the disclosure, but the stock was even at $96 in morning trading Thursday. 

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