Twitter‘s new Chief Executive Officer Linda Yaccarino has begun her role at the social media company, she tweeted late on Monday, about a month after Elon Musk named her as the new CEO.

“It happened — first day in the books!,” she tweeted, without providing further details, a Reuters report said.

Yaccarino, the former advertising chief at NBCUniversal, is taking over Twitter at a time when the social media platform has been trying to reverse a plunge in ad revenue.

Musk, who has served as the CEO since his $44 billion buyout of Twitter last October, previously said that Yaccarino would help build an “everything app”.

Former NBCUniversal executive Joe Benarroch also joined Twitter on Monday. He oversaw communication strategy for the Comcast-owned company’s Advertising and Partnerships division, reporting to Yaccarino, before joining Twitter.

Meanwhile, earlier in the month, Twitter’s head of trust and safety, Ella Irwin, said she has resigned from the social media company, which has faced criticism for lax protections against harmful content since billionaire Elon Musk acquired it in October.

Irwin, who joined Twitter in June 2022, took over as head of the trust and safety team in November when previous head Yoel Roth resigned. She oversaw content moderation, an earlier Reuters report had said.

Since Musk’s acquisition, Twitter has cut costs dramatically and laid off thousands of employees, including many who had worked on efforts to prevent harmful and illegal content, protect election integrity, and surface accurate information on the site.

Musk has promoted a feature called Community Notes, which lets users add context to tweets, as a way to combat misleading information on Twitter.

The company is also facing increasing scrutiny from regulators over its moderation efforts.

Twitter withdrew from a voluntary agreement with the European Union to tackle disinformation, while saying it was committed to complying with upcoming internet rules in the EU.