A security flaw in the web version of WhatsApp exposed "hundreds of millions" of accounts to hackers, according to a report from Check Point. The flaw allowed an account to be taken over through a single malicious message.
Opening the sent file could have let hackers see an account's conversations, photos, videos, contacts, and more. The users were vulnerable because of a flaw in the app's end-to-end encryption.
Attackers could potentially download your photos and or post them online, send messages on your behalf, demand ransom and even take over your friends' accounts, - Check Point
The same flaw was found in Telegram, another messaging app. Both have fixed the issue.