From Sophos:

At the time of writing, Sophos has received no reports from users affected by this Trojan. However, we have issued this advisory following enquiries to our support department from customers.

Customers using EM Library, Enterprise Console, PureMessage or any of our Sophos small business solutions will be automatically protected at their next scheduled update.

Information about Troj/EMDoor-A can be found at: http://www.sophos.com/virusinfo/analyses/trojemdoora.html