Go to http://sophos.williams.edu.

Simply download and mount the DMG by double clicking it and then install.
Upon completion, you must enter some information to tell Sophos how to receive updates:
1 - Click on the blue shield near the clock, choose 'Open Preferences.'
2- Click on the AutoUpdate tab.
3 - Click on the lock in the left hand corner and enter your Mac's username and password. 4 - Choose 'Company web server' and enter the URL: http://sophos.williams.edu/ESOSX
Lastly, click 'Set' and right click on the blue shield and choose 'Update Now'

To enable real-time disinfection, you must click on the blue shield, 'Open Preferences', on Scanning tab choose Disinfection from drop down. Unlock the shield in lower left window, authenticate and choose 'Enable Disinfection'. Now click on 'Action on infected files.' If performing an manual scan you should configure Sophos on demand scanning by clickingthe blue shield, opening Sophos Anti-Virus, clicking on 'Disinfection' and then clicking on 'Enable Disinfection' and then selecting the 'Action On Infected Files' check box.