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For Facebook, a signature from Cambridge Analytica whistleblower Christopher Wylie was enough proof -- a decision that would come back to bite the social network.

When Facebook learned about Cambridge Analytica buying 87 million people's profile information without user permission in 2015, the social network's executives said it requested the data be deleted. Facebook said that it received "certifications" that had happened, but now says it's learned the UK-based data profiling firm lied.

During a Senate Judiciary committee hearing on Wednesday, Wylie, a former Cambridge Analytica employee and whistleblower who detailed the extent of the company's data collection in March, told senators what that certification entailed.

Wylie said he received a letter in 2016 from Facebook, writing that they knew he still had data from Cambridge Analytica's harvesting program, and asked him to delete it.

"It requested that if I still had the data to delete it and sign a certification that I no longer had the data," Wylie said. "It did not require a notary or any sort of legal procedure. So I signed the certification and sent it back, and they accepted it."

It appeared as simple as a signature for Facebook to determine that Wylie no longer had data on millions of people without their permission.

A Facebook spokesman confirmed Wylie's remarks, and said, "As we've said multiple times, we sought signed certifications from each of the parties that the data had been deleted."

More than a year after Facebook's signed certifications requests, the company's light standard of scrutiny has come back to haunt it.

The scandal with Cambridge Analytica has brought data privacy issues with Facebook into the spotlight, setting off a #DeleteFacebook campaign on social media and sending Facebook CEO Mark Zuckerberg to testify before Congress in April. Zuckerberg is also set to testify before the European Parliament as soon as next week.

Two months after the scandal first broke, Facebook is still facing the backlash. During the hearing, Sen. Kamala Harris, a Democrat from California, called out how much data the social network collects on up to 2.2 billion people.

"Users have little to no idea just how Facebook collects their data, including tracking the user's location or device they are using, their IP address and activities on other websites," Harris said. "In the real world. This would be like someone following you every single day as you walk down the street, watching what you do, where you go, for how long, and with whom you're with."

She called for lawmakers to step in, pointing out that "few Americans can decipher or understand" privacy policies from social networks.

Wylie noted in his testimony that using social media "is not really a choice for most people." He noted how essential it is to many people's livelihood and friendships, and urged social networks to create policies that ensure safety for the massive amount of people who depend on it.

"We don't allow car companies to make unsafe cars and just put terms and conditions on the side of that car," Wylie said.

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