Already being discussed here: OS X Backdoor Trojan in Beta
It's just Sophos trying to scare people into buying their software. The trojan doesn't yet exist and can easily be avoided with common sense.
The Mac product has been available for a while I believe. I have tested their A/V products for both windows and Mac, although the Mac product actually wasn't too bad, their windows products are horrible and expensive to say the least! Almost all major a/v vendors have Mac products now, they are just not advertised or easy to find on their sites.
