Twitter has made a startling admission. In a frank disclosure posted in its help section, the social network revealed that it may have used emails and phone numbers submitted for two-step security authentication for targeted advertising.

It stated that the data may have been wrongly submitted for use in its Tailored Audiences and Partner Audiences advertising system.

"Tailored Audiences is a version of an industry-standard product that allows advertisers to target ads to customers based on the advertiser's own marketing lists. Partner Audiences allows advertisers to use the same Tailored Audiences features to target ads to audiences provided by third-party partners," it said.

"When an advertiser uploaded their marketing list, we may have matched people on Twitter to their list based on the email or phone number the Twitter account holder provided for safety and security purposes. This was an error and we apologise."

Twitter claims that it is currently not possible to know how many people were affected by the error. It says that it has addressed the issue so that it will not happen again.

"We’re very sorry this happened and are taking steps to make sure we don’t make a mistake like this again," it added.

Those worried about the "error" and want to ask Twitter questions can contact the network's office of data protection by filling in a form that can be found here.

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