Facebook and WhatsApp have received a letter from the US Federal Trade Commission reminding them about user privacy.
In February, Facebook announced that it was planning to acquire messaging service WhatsApp in a deal worth $16 billion (£9.6 billion).
Google and BlackBerry have both confirmed that aspects of their mobile software are affected by the Heartbleed bug.
Heartbleed, which became public last week, exploits a flaw in the OpenSSL software. OpenSSL is one of the options for protecting online information and preventing criminals from ‘listening in’ to internet traffic.