DO NOT PANIC! I am not claiming you are subject to attacks if you happen to be a Mac user. I do not know that this is the case.
The University of North Dakota just announced that Mac users will need to install virus software if they want to use the University network after Feb. 19. No specific threat was identified in the email. My assumption is that Mac users may pass on Windows viruses. This is kind of like asking everyone to get a flu shot even though some feel that they are not going to be harmed if they should get the flu. All can be carriers.
Mac users were recommended to use the free antivirus ClamXav.
I noticed that the install instructions asked that users back up first. I have had one issue playing with a previous version of ClamX. The virus protection found a virus in my downloaded email and messed up this email in removing the virus. As I understand the issue, email storage (at least at that time) is kind of a blob (sorry for the imprecise terminology) rather than easily differentiated files. Hence acting on the virus prevented me from using the client to access the email that had been downloaded to my computer.
I am encouraging my colleagues who do not run a backup program to purchase an external hard drive and use Time Machine.