Para acabar com algumas duvidas e evitar sempre a mesma resposta a cada vez que esta questão se põe ("ninguem" usa MAC por isso é que n há virus), achei interessante colocar aqui isto... "There is no silver bullet answer as to why not, its a combination of reasons : 1. OS X is built on UNIX. UNIX was a multi user system with a security architecture built into it at the beginning. WINDOWS came from a single user architecture with security and multi user capability as an after thought. 2. UNIX had networking built into it from the beginning, again in Windows this was bolted in at a later date. 3. Windows built Internet Explorer into the O/S at a very deep level, and allowed code execution within the browser. In OS X the browser is a completely separate application, its not a integral part of the OS. IMHO, this is the fundamental screw-up Microsoft made, as they created so many hooks into which someone can attack the OS. 4. In earlier Windows everything ran as the system user, so the capability to compromise an entire system was easier. (see reason 1) 5. Microsoft’s backward compatibility mantra doesn’t do them any favours as to run old software they need so many old APIs, all of which can have holes in them. 6. OS X has no registry. IMHO, second fundamental flaw Microsoft made. 7. OS X asks for your password before allowing you to run new software or install something. Not fool proof, but at least fool resistant. Personally I don’t buy the “lack of market share” reason. Consider that in pre OS X days Macs did have viruses. Also interesting, that at that stage Macs were suffering point 1 & 2. No system is totally safe, but Macs have a lot of architecture working in their favor."