Twitter on Saturday blocked searches for a series of hashtags and keywords used to promote the sale of child sexual abuse material (CSAM) following an investigation by NBC News published the previous day.

NBC News discovered that a series of hashtags on the platform related to the Mega file-sharing service served as rallying points for users looking to trade or sell MASI. NBC News looked at the hashtags over a period of several weeks and counted dozens of users collectively posting hundreds of tweets a day.

Accounts used thinly disguised MASN-related keywords and terms to promote content they said was stocked on Mega, which they said was available to purchase or trade.

Twitter prohibit any promotion of CSAM on his platform, and since CEO Elon Musk took over the company, he has been outspoken in criticizing former company leaders, claiming they didn’t do enough to address child sexual exploitation material on the platform. Musk said in November that cleaning up the platform and addressing child exploitation on it was his «No. 1 priority.»

NBC News’ examination of the hashtags found that some accounts had been using them for months and that dozens of users had tagged Musk using the hashtags to alert him to the problem. However, the hashtags appeared to remain largely unmoderated until Saturday.

Following the NBC News report on Friday, Ella Irwin, Twitter’s vice president of trust and product safety, which includes oversight of child safety on the platform, said in an email: «We will do an additional targeted review this weekend. and we’ll see what we find. As you probably know, the links you shared relate to a file-sharing service widely used for a wide variety of purposes, making it much more difficult to find the specific illegal content being posted with the hashtags in question.»

In a follow-up email on Saturday, Irwin said he met over the weekend with his team and decided to ban the hashtags, which he said the company had been reviewing.

“We were already looking at doing this in the coming weeks as we have banned other commonly used hashtags for traffic. [CSAM] material already, however, we made the decision to expedite this action for these terms,” he said.

Irwin said that in the last six weeks Twitter had been analyzing thousands of hashtags for a project that was scheduled to be completed in the next few weeks. He noted that the company did not want to ban hashtags that had legitimate use, but in this case the company decided to act.

“If bad actors successfully evade our detection using these specific terms and despite our currently implemented detection mechanisms, then we would prefer to make it much more difficult to do this on our platform,” Irwin wrote.

In a review of hashtags and tweets last week, NBC News confirmed that searches related to file-sharing site Mega had been blocked. Other hashtags related to different crypto platforms and other keywords associated with CSAM were still active.

In an email on Friday, Mega Chief Executive Stephen Hall said the New Zealand-based encrypted service had a zero-tolerance policy towards CSAM. «If a public link is reported to contain CSAM, we immediately disable the link, permanently close the user’s account and provide full details to New Zealand and any relevant international authorities,» Hall wrote.

In an email on Tuesday, Hall reacted to the news that Mega-related terms were blocked on Twitter by writing that it was «a pretty forceful reaction to a complex situation.»

Despite Musk’s claims that he is prioritizing the removal of MASI on Twitter, the layoffs and staff reductions appear to be strangling the company’s Trust and Safety group, which houses employees who oversee child safety.

According to Securities and Exchange Commission documents and internal records obtained by NBC News, less than half of the employees now work in confidence and security at the company than they did at the end of 2021. According to Bloombergthe trust and safety team suffered further cuts this month.

A former employee who asked to remain anonymous because he had signed a confidentiality agreement said that many of the employees specifically tasked with child safety issues had left the company.

Irwin said in an email that Twitter has «approximately 25% more staff in this issue/problem space now than the company it had at its peak last January.» She said that “many employees who were on the child safety team last year are no longer a part of the company, but that was mostly between January and August of last year due to the rapid attrition Twitter experienced across the company.”