Wall Street is reacting to a New York Times report that Cambridge Analytica gained unauthorized access to data from more than 50 million Facebook, Inc. (Nasdaq: FB ) users. Facebook says the data was improperly shared rather than hacked, but the stock was down 4 percent early Monday as investors feared more data security concerns could impact the company's bottom line.

Cambridge University psychology professor Aleksandr Kogan reportedly obtained the data from Facebook users via an app called "thisisyourdigitallife." Facebook users used the app to fill out a questionnaire to create a psychological profile.

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However, that data was reportedly then shared without Facebook's permission with Cambridge Analytica, a private company which worked to develop Facebook ads for President Donald Trump during the 2016 campaign.

Facebook says it was told the data Kogan collected was destroyed.

In a blog post on Sunday, Facebook deputy general counsel Paul Grewal said it is inaccurate to classify the incident as a "breach" because users knowingly gave Kogan access to the data.

"The claim that this is a data breach is completely false," Grewal wrote. "Aleksandr Kogan requested and gained access to information from users who chose to sign up to his app, and everyone involved gave their consent."

Regardless of how the incident is classified, Facebook's massive trove of data on more than 2 billion global users is a growing concern for regulators and investors. In May, Europe is taking a major step in protecting user data on Facebook and other social media platforms by implementing the General Data Protection Regulation, which is aimed at giving users more control over their personal data.

Facebook's data is critical for its advertising business, which accounted for $12.78 billion of Facebook's $12.97 billion in total revenue in the most recent quarter.

GBH Insights head of technology research Daniel Ives says Facebook investors should certainly keep an eye on how this latest data incident plays out.

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"The concern from the Street's perspective is this latest fiasco could reignite the debate within the beltway and EU around a tighter regulatory environment Facebook and its social platform brethren could face going forward," Ives says. "Ultimately we believe this is more headline risk at this point and does not overly concern us this would lead to major changes/impact to the company's advertising fortress and key monetization engine for 2018 and beyond."

GBH has a "highly attractive" rating and $225 price target for FB stock .

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