Former Twitter security chief Peiter “Mudge” Zatko a wild card in Elon Musk’s billionaire deal, on Tuesday is set to testify before a US Senate committee looking into whether security practices at Twitter were dangerously lax.

Senators who will hear Zatko’s testimony before the Senate Judiciary Committee are alarmed by his Twitter allegations at a time of heightened concern over the safety of powerful tech platforms.

This is Zatko’s second Capitol Hill appearance, and first in 21st-century. In 1998, he testified before a Senate panel along with fellow members of a hacker collective who warned about the security dangers of the then-emerging internet age.

Sen. Dick Durbin, the Illinois Democrat who chairs the panel, has said that if Zatko’s claims are accurate, “they may show dangerous data-privacy and security risks for Twitter users around the world.”

Peiter “Mudge” Zatko, a hacker and an American cybersecurity expert was hired by Jack Dorsey in 2020 after Twitter suffered a massive cyber attack. Zatko remained the security head of the company from November 2020 to January 2022.

On Monday, a majority of Twitter Inc’s shareholders have voted in favor of the social media company’s $44 billion sale to Elon Musk, people familiar with the tally said. Shareholders were widely expected to vote in favor after a stock market downturn made Musk’s $54.20-per-share deal for Twitter, which was signed in April, look pricey in the current environment. Twitter shares are now hovering around $41.