Signal saw 7.5 million downloads following WhatsApp's announcement, a 4,200% increase on the previous week. Telegram downloads surged 91%.
WhatsApp's rivals got a massive boost after the messaging app announced on Wednesday it would make users share some personal data with its parent company Facebook.
WhatsApp told users they would have to agree to let Facebook and its subsidiaries collect WhatsApp data — including phone numbers and locations — before February 8, or else lose access to the app. WhatsApp has since clarified this only affects users outside of the EU and UK, and said that the change "does not affect the privacy of your messages with friends or family in any way."
Data from app analytics firm Sensor Tower shows Signal, a rival encrypted messaging service, saw an enormous surge in user numbers following WhatsApp's announcement.
"From January 6 to January 10, Signal saw approximately 7.5 million installs globally from across the App Store and Google Play," a Sensor Tower spokesperson told Insider.
This represented a 4200% increase on the previous week.
Signal received significant publicity following WhatsApp's announcement, with public figures including Elon Musk
and Edward Snowden endorsing the app. Musk tweeted "use Signal," which had the unexpected side-effect of sending stock for an unrelated company, Signal Advance, soaring by 11,700%.
Encrypted messaging service Telegram saw even more users flock to its service. In the same time period, it amassed 9 million new users, up 91% from the previous week.
For both Signal and Telegram, the biggest growth market was India. Signal saw 2.3 million installs in India — more than 30% of its total new installs. India accounted for 1.5 million of Telegram's installs, or 16% of all installs.
For Signal, the second biggest market was the US, where users installed it about 1 million times.
WhatsApp has scrambled to try to allay public concerns about its app's privacy since Wednesday. "We want to address some rumors and be 100% clear we continue to protect your private messages with end-to-end encryption," the company said in a statement on Monday.
"We want to be clear that the policy update does not affect the privacy of your messages with friends or family in any way. Instead, this update includes changes related to messaging a business on WhatsApp, which is optional, and provides further transparency about how we collect and use data," WhatsApp added in an FAQ on its website.
Two crossed lines that form an 'X'. It indicates a way to close an interaction, or dismiss a notification.