By Zoe Kleinman, BBC

Message platforms Signal and Telegram have both seen a huge surge in downloads around the world following a controversial update to WhatsApp's terms and conditions.

WhatsApp has told its two billion users they must allow it to share data with its parent company Facebook if they wish to continue using it.

This does not apply to users in the UK and Europe.

However, the notification has been sent to everyone.

All WhatsApp users will be unable to continue with the service unless they accept the new terms by 8 February. The platform said the update will enable it to offer features such as shopping and payments.

It also said its practice of sharing data with Facebook was not new.

Both Telegram and Signal also offer free-to-use encrypted messaging services.

Signal strength

According to data from analytics firm Sensor Tower, Signal was downloaded globally 246,000 times the week before WhatsApp announced the change on 4 January, and 8.8 million times the week after.

This included big surges in India, where downloads went from 12,000 to 2.7 million, the UK (from 7,400 to 191,000) and the US (63,000 to 1.1 million).

In a series of tweets, Signal said some people were reporting issues with creating groups and delays to verification codes arriving because of the rapid expansion but that it was solving the issues.

"Our new servers are ready to serve you," it said on 10 January.

We continue to shatter traffic records and add capacity as more and more people come to terms with how much they dislike Facebook's new terms. If you weren't able to create a new group recently, please try again. New servers are ready to serve you.

— Signal (@signalapp) January 10, 2021

It also received endorsement from Tesla co-founder Elon Musk, who tweeted "use Signal" on 7 January.

Telegram soars

Telegram has proved even more popular, with downloads booming globally from 6.5 million for the week beginning 28 December to 11 million over the following week.

In the UK, downloads went from 47,000 to 101,000. And in the US they went from 272,000 to 671,000.

During the same period, WhatsApp's global downloads shrank from 11.3 million to 9.2 million.

Even so, one industry watcher said he did not think this necessarily represented a big problem for WhatsApp, which has been downloaded 5.6 billion times since its launch in 2014.

"It's going to be difficult for rivals to break user habits, and WhatsApp will continue to be one of the world's most popular and widely used messaging platforms," said Craig Chapple, mobile insights strategist at Sensor Tower.

"It'll be interesting to see whether this latest trend sticks, or users revert back to what they know."

WhatsApp has said the data it shares with its parent company does not 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 location of a user's internet connections

• any payments and financial transactions made over WhatsApp

It said its policies were in line with "applicable" privacy laws.