If you have an AccountRight installation CD, insert this into your computer's CD drive and follow the installation instructions.
If you have a current AccountRight subscription, you can download AccountRight and the installation instructions from my.myob (Australia | New Zealand). Make sure you download the "Full Install" file, not the upgrade. If you need help accessing or using my.MYOB, see Downloading AccountRight from my.MYOB.
Once AccountRight has installed, you can turn your antivirus software back on.