Twitter Faces Legal, Political Peril in Whistle-Blower Case (2)

A whistle-blower complaint from Twitter Inc.’s former head of security, claiming severe shortcomings in the social media company’s handling of users’ personal data, will have wide ramifications for the business.

US lawmakers vowed to investigate, and the legal team for Elon Musk, who is seeking to abandon his agreement to acquire Twitter, was emboldened by the claims. Twitter shares fell as much as 5% on Tuesday, the biggest intraday drop in more than a month.

The former executive, Peiter Zatko, alleged “egregious deficiencies” in Twitter’s defenses against hackers and other lax approaches to security, according to a ...