Twitter Inc faced questions on Friday about its approach to internal security after a company employee briefly deactivated U.S. President Donald Trump’s account.

The 11-minute blackout of the @realDonaldTrump account late on Thursday drew widespread attention on the microblogging site. Twitter is already grappling with criticism of its handling of account suspensions, user abuse and changes to its terms of service.

Twitter on Friday declined to answer questions including how many employees can suspend an account or what special protections there are for high-profile users like Trump.

“We are not going to be able to publicly discuss these kinds of things,” a company spokesman said.

Trump often uses Twitter to comment on political and military matters. Twitter users expressed concerns that employee interference or technology glitches involving his account could threaten national security.

Security experts had previously speculated Twitter could have installed special protections on Trump’s account, such as the ability to only access it from certain devices.

“We have learned that this was done by a Twitter customer-support employee who did this on the employee’s last day. We are conducting a full internal review,” Twitter said in a tweet late on Thursday.

“We are continuing to investigate and are taking steps to prevent this from happening again,” the company said in an earlier tweet.

Reuters could not determine how many Twitter employees had the authority to delete accounts or tamper with them in other ways, such as by sending bogus Tweets.

Speaking on condition of anonymity, a former Twitter employee said it was unlikely a worker with suspension privileges would also be able to hijack an account to send out messages.

“Different types of access,” the former employee said. “I‘m not sure anyone at Twitter can tweet from someone else’s account.”

The company on Friday separately announced minor updates to its rules, the latest in a string of changes designed to improve user experience.

Twitter shares were up 0.3 percent in morning trading.

Trump, who has nearly 42 million Twitter followers, responded to the temporary loss of his account by boasting about his wide reach on the service.

“My Twitter account was taken down for 11 minutes by a rogue employee,” Trump said on Twitter early on Friday. “I guess the word must finally be getting out-and having an impact.”

He has used Twitter to attack opponents and promote his policies, both during the 2016 presidential campaign and since taking office in January.

Thursday evening’s incident also raised questions about how Twitter secures the official @potus presidential account and other accounts that could potentially influence world events.

Technology companies including Twitter are meanwhile under attack from U.S. lawmakers for failing to stem the spread of Russian propaganda and misinformation on their platforms.

Twitter in particular has long been criticized for not doing enough to police its platform and respond to complaints of abuse.

The temporary deletion of the Trump account sparked a flood of criticism from Twitter users, though many of the president’s critics also said they were happy to see the account disabled.

In 2013, hackers took control of the main account for the Associated Press and tweeted that explosions at the White House had injured then-President Barack Obama, causing stocks to briefly plunge.