Facebook as we know it has always been a free product.

But as the social media giant's massive data scandal has highlighted, a free Facebook membership has always come with a cost.

Put simply, the firm's two billion-plus users have been able to use the site without paying in exchange for surrendering a wealth of personal information to advertisers, according to the Daily Mail.

According to Facebook COO Sheryl Sandberg, that business model is unlikely to change unless users are willing to pay up.

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Facebook collects mountains of data on users, ranging from phone numbers and text messages, to addresses and other demographic information, down to your specific interests.

That information is then made available to a wide network of brands who can use it to serve up targeted advertisements both on and off Facebook.

Users can change their privacy settings, but in order to opt out of Facebook's targeted advertising completely, they'll have to pay, Sandberg said in an interview with NBC News on the Today Show.

"We don't have an opt-out at the highest level," Sandberg explained.

"That would be a paid product," she said.

Sandberg added Facebook doesn't sell user data but that "our service depends on your data".

Facebook CEO Mark Zuckerberg and Sandberg have been making the rounds in recent days to discuss what steps the firm is taking to regain users' trust and prevent data from being misused in the future.

In the wake of the Cambridge Analytica scandal, which revealed at least 87 million members' data had been harvested without their knowledge, more and more users have been rushing to protect their personal information.

Sandberg said Facebook is continuing to conduct an internal investigation into how Cambridge Analytica obtained the data.

In the process of the audit, she warned that more damaging information could be uncovered.

"I'm not going to sit here and say that we're not going to find more because we are," Sandberg explained.

She also admitted that the firm should have been more proactive about notifying the public sooner.

"We were given assurances by them years ago that they deleted the data," Sandberg said.

"We should've followed up. That's on us," she added. "We are trying to do a forensic audit to find out what they have".

Sandberg said in an separate interview with Bloomberg that several brands had "paused" spending on digital advertising with Facebook for the time being.

However, Zuckerberg has reassured investors that the privacy scandal hasn't negatively impacted its user count or ad business.

Earlier this week, Zuckerberg took the blame for the data row, saying only he could fix it.

He added that it will 'take a few years to fix Facebook's privacy issues.

"I think we will dig through this hole, but it will take a few years. I wish I could solve all these issues in three months or six months.

"But I just think the reality is that solving some of these questions is just going to take a longer period of time."

After repeated calls from legislators and officials, Zuckerberg has agreed to testify on the matter next Tuesday and Wednesday during two US congressional hearings.