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The company said it recently discovered that when it asked users to provide an email address or phone number to beef up safety and security, this information may have been used in its Tailored Audiences and Partner Audiences advertising system – which allows companies to target ads to customers.
Twitter said it matched users based on email or phone number to advertiser uploaded marketing lists as “an error.” No personal data was shared externally with partners or third parties.
The company is not certain how many users were affected. It corrected the problem on Sept. 17.
The mistake comes amid growing concerns over privacy in the technology sector – as federal regulators probe the country’s largest companies. The House of Representatives and the Federal Trade Commission have both launched investigations into Facebook, after it was fined $5 billion by the FTC over privacy abuses.