Updated on March 31, 2015: Clarify 4.5 release timeframe and manual update section

We are planning to discontinue support for 32 bit Macs for Tor Browser.

We're doing this for two main reasons. First, Apple itself no longer supports 32 bit Macs. The only remaining 32 bit Mac users are on OSX 10.6, which Apple ended support for in February 2014. Second, 64 bit software has improved security properties by way of improved address space layout randomization (ASLR), which makes exploitation more difficult.

This transition will happen in phases: First, the upcoming 4.5-alpha series will only be available as 64 bit builds. We will continue releasing 32 bit versions of the 4.0 series until the 4.5 series is declared stable. When the 4.5 release stabilizes, all support for 32 bit Macs will end. The 4.5 release series will become stable in mid-April of 2015. This means that 32 bit Mac users should begin investigating their options now.

Not all 10.6 Mac OS users are on 32 bit systems. According to Apple's support website, only two CPU models (the Intel Core Solo and the Intel Core Duo) were released that can not run 64 bit code. As long as you do not have those processors, your Mac should be able to run the 64 bit Tor Browser 4.5 just fine. However, we strongly encourage you to upgrade to a newer version of Mac OS even so, as you are not receiving security updates.

If your hardware is not 64 bit capable or your system won't run Tor Browser 4.5, you should still be able to use Tails, which contains the Tor Browser. You can run Tails in a virtual machine such as VirtualBox, or you can manually install it to a USB disk from the Mac OS Terminal. If you install Tails to a USB stick, you will need to reboot your Mac in order to use it.

10.6 and 10.7 Mac Users: Manual Update Required

Most Mac users should should be updated to the new 4.5 series automatically by the in-browser updater in mid-May 2015. However, due to technical limitations with determining the ability of early Mac systems to properly run 64 bit programs, we are unable to safely and reliably determine if Snow Leopard (10.6) or Lion (10.7) Mac users will successfully be able to run a 64 bit Tor Browser update, and so we have disabled the in-browser updater for those versions.

This means that you must perform this update manually, as you had to do prior to the 4.0 series. To do this, download the 4.5 DMG and drag the new 64 bit Tor Browser 4.5 over your old Tor Browser 4.0, and replace the application. Again, if the new 64 bit Tor Browser does not function on your system, we recommend using Tails, as described above.

Once you are running the 64 bit version, updates should function correctly again.