The firm said it took down the link for credit report assistance temporarily "out of an abundance of caution".
The Equifax may have been hacked again, now to serve up adware.
"We are aware of the situation identified on the equifax.com website in the credit report assistance link", Equifax spokesman Wyatt Jefferies said in a statement.
Ars Techica reported that an independent security analyst had discovered Wednesday that hackers had manipulated part of the credit-reporting giant's website to push out malicious, fraudulent Adobe Flash updates to visitors.
The incident comes just over a month after Equifax disclosed a massive data breach in which hackers stole the personal information of more than 145 million US consumers.
Equifax's stock plunged at the news of the latest breach, a Wall Street Journal reporter noted on Twitter.
If suffering one of the worst hacks in history wasn't enough, Equifax may have been attacked yet again.
What personal information was stolen in the hack? .
Somehow, the worst credit-card-data breach in US history just got worse.
Equifax's security protocols have been under scrutiny since September 7 when the company disclosed its systems had been breached between mid-May and late July. Not only is the service free, but Credit Karma lets you access your credit scores and reports without charge as many times as you like. But lawmakers and several federal agencies, including the FBI and the Federal Trade Commission, are investigating the company's response to the breach, why it took Equifax more than a month to notify the public and whether executives engaged in insider trading.