Messaging platform Signal says it's resolved technical problems that have hampered its service over the past few days, after seeing a rush of latest users.
On Friday, some users reported messages failing to forward both the mobile and desktop apps for several hours.
The company has seen an enormous uptick in interest since its rival WhatsApp unveiled new privacy terms last week.
It urged users to continue with the service and report any longer problems.
In a series of tweets, it said users might see errors in a number of their chats, including missed messages, but this is able to not affect their security.
"Signal is back!" it said.
"Like an underdog browsing a training montage, we've learned tons since yesterday - and that we did it together.
"Thanks to the many new Signal users around the world for your patience."
Both Signal and Telegram, another free-to-use encrypted messaging app, have benefited from discontent sparked by WhatsApp's updated terms and conditions.
WhatsApp told its two billion users they need to allow it to share data with its parent company Facebook if they wished to continue using it.
This doesn't apply to users within the UK and Europe - but the notification was sent to everyone.
WhatsApp and Facebook to share data outside Europe
WhatsApp stressed that its practice of sharing data with Facebook wasn't new, and wasn't being expanded. It said there had been "confusion" about its message, which initially gave people until 8 February to simply accept its updated terms or stop using the service.
WhatsApp has now changed the deadline to fifteen May, saying it might use the time to clear up misinformation.
"We can't see your private messages or hear your calls, and neither can Facebook," WhatsApp said in an earlier FAQ blog post.
According to data from analytics firm Sensor Tower, Signal was downloaded 246,000 times worldwide within the week before WhatsApp announced the change on 4 January and 8.8 million times the week after.
In India, downloads went from 12,000 to 2.7 million. In the UK, they leaped from 7,400 to 191,000, and within the US from 63,000 to 1.1 million.
On Wednesday, Telegram said it had surpassed 500 million active users globally. Downloads jumped from 6.5 million within the week starting 28 December, to 11 million during the subsequent week.
During an equivalent period, WhatsApp's global downloads shrank from 11.3 million to 9.2 million.
What does WhatsApp share with Facebook?
WhatsApp has said the info it shares from users outside the EU and UK doesn't include messages, groups or call logs.
However, it does include:
- phone number and other information provided on registration (such as name)
- information about the user's phone, including make, model, and mobile company
- internet protocol (IP) addresses, which indicate the situation of a user's internet connections
- any payments and financial transactions remodeled WhatsApp