While helping answer computer security questions at different site a common question I see asked is can Macs get viruses. Now most of the time I see others post that they can but every once in a while people post on there that Macs are immune to malware.
Now I would like to make it clear, in my opinion Macs can get malware. Now most people I would say know that, but most people (in my opinion) do not know why they don't get them as often as Windows machines. The reason is Malware writers create malware based on Market Share. Since Windows has the largest market share of PC Operating Systems it quickly becomes a top target of malware writers. This is no way makes Mac machines more immune then Windows. Some malware is already out there for Mac machines but since a majority of the people you know most likely are on a Windows machines you do not hear much about it.
Recently Mobile OSes have started getting more malware also. As people jump to Smartphones to store personal data the malware writers have jumped with them to steal this personal data. Malware spreading through social networks has also jumped recently as more people jump to social networks.
Remember no OS (so far) is Immune to all malware.