SAN FRANCISCO (BLOOMBERG) - Twitter is under investigation by the Federal Trade Commission for using phone numbers uploaded for security purposes to target people with advertising.

Twitter received a draft last week of a complaint from the FTC alleging that the social media company violated a 2011 consent decree in which it agreed to better protect users' personal data, the company said on Monday (Aug 3) in a regulatory filing.

The probe may lead to a "probable loss" of US$150 million (S$206 million) to US$250 million, the San Francisco-based company said in the filing.

"The matter remains unresolved and there can be no assurance as to the timing or the terms of any final outcome," Twitter said in the filing.

"Following the announcement of our Q2 financial results, we received a draft complaint from the FTC alleging violations of our 2011 consent order," a Twitter spokesperson said. "Following standard accounting rules we included an estimated range for settlement." A spokeswoman for the FTC declined to comment.

Twitter's 2011 settlement with the FTC barred the company for 20 years from "misleading consumers about the extent to which it protects the security, privacy, and confidentiality of non-public consumer information."

Twitter confirmed in 2019 that it was using phone numbers provided to the company for security purposes to target those users with advertising. At the time, Twitter said those numbers were used "inadvertently," and added that it did not know how many user's were impacted.

The current complaint alleges the company violated the terms of the agreement by misusing phone numbers or emails "during periods between 2013 and 2019," according to the filing.