The company has seen a surge in turnout since its rival WhatsApp revealed new privacy provisions last week.
Signal said, on Twitter, that it was adding servers “at a record pace” and was working to restore service.
“Millions and millions of new users send a message stating the importance of privacy,” she said in a tweet.
Both Signal and Telegram, another free encrypted messaging app, have taken advantage of the discontent caused by WhatsApp’s updated terms and conditions.
WhatsApp told its two billion users that they should allow it to share data with its parent company, Facebook, if they want to continue using it.
This does not apply to users in Britain and Europe, but the notice was sent to everyone.
WhatsApp stressed that its practice of sharing data with Facebook is not new, and has not been expanded. She said there was “confusion” about her message, which initially granted people until February 8th, to accept its updated terms or stop using the service.
WhatsApp has now changed the deadline to May 15, saying it will use the time to clear the misinformation.
WhatsApp said in a previous post in the FAQ blog: “We cannot see your private messages or hear your calls, as well as Facebook.”
According to data from Sensor Tower, 246,000 people downloaded the Signal app worldwide in the week before WhatsApp announced the change on January 4, but that number jumped to 8.8 million the following week.
On Wednesday, Telegram said it had surpassed 500 million active users globally. Downloads jumped from 6.5 million in the week that began on December 28, to 11 million the following week.
During the same period, global WhatsApp downloads shrank from 11.3 million to 9.2 million.