I have said to many people previously: yes they do exist, no it’s not a major problem at the moment but may become one as Macs become more popular, and like Windows it highly depends on your behaviour.
The Virus examples Sophos provide:
- Dodgy software from legitimate looking websites.
- Disguised as Pirated software
- Dodgy web plugins that claim to be required.
- Twitter links (that may also require dodgy web plugins)
Simple: keep up with updates, only install software and web plugins recommended by friends and/or major trusted websites. On the subject of web plugins, for most usage you only need Flash and even that is becoming less of a requirement. If you view a lot of video online you may also need DivX web player (commonly targeted) and on rare occasions Microsoft Silverlight.