Apple has released a patch for the Shellshock bug. If you don’t know what this bug is, take a few minutes to find out about it here and then head over to one of these links, depending on which version of OS X you are running (10.7.5 Lion, 10.8.5 Mountain Lion, 10.9.5 Mavericks) and apply the patch.
If you are unsure which version of OS X you are running, just click the apple in the top left corner of your screen and press About This Mac.
We take security issues very seriously so please, don’t just dismiss this.