Twitter has purchased year-old Android security start-up Whisper Systems for an undisclosed sum.

Whisper Systems offers security and management solutions such as encryption to enable mobile devices to become enterprise ready.
It was co-founded by well-known researcher Moxie Marlinspike.
"Now that we have been acquired by Twitter, we're looking forward to integrating our technology and our expertise into Twitter's products and services," Marlinspike wrote on the Whisper Systems blog.
As a result of the deal, however, Whisper must take its product line offline. First to go is RedPhone, its voice encryption product for the Android. Flashback, which stores encrypted backups, is expected to be disconnected next month.
RedPhone was created to allow Egyptians to place phone calls and avoid avoid interception during the Arab Spring uprisings earlier this year.
Marlinspike responded in a tweet to concerns the temporary RedPhone switch-off could affect lives and said that it was "certainly a priority for me to get it back online as quickly as possible".
A Twitter spokesperson did not respond to a request for comment. It is unclear how the microblogging service will implement Whisper's solutions into its product line. Prior to the acquisition, all of Whisper's source code was available for review.
The blog post said Whisper was launched because its creators were concerned that mobile devices would suffer the same threat-filled fate as the traditional desktop environment.
"We ended up tackling the full stack -- all the way from application-level solutions at the top of the stack, down through a hardened version of Android, to kernel modifications at the bottom of the stack," the blog entry said. "Along the way, we learned a lot, and developed products that we're proud of."
With Darren Pauli