One of the great things about surfing the Internet with a Mac was that you didn't have to worry about catching malware, spyware, and/or viruses from visiting sketchy web pages. Note that I said didn't: Things have changed. Go to the wrong porn site on a Mac and you can have your Mac infected. Historic!
Now, don't panic, all you pr0n m0nkeys out there; all is not lost.
The infection is caused by what's called a trojan (and you guys probably aren't wearing one, seeing as you're surfing porn rather than spooning with a real-live SO) is avoidable. A trojan is a malicious program disguised as sweetness, light, and all-things-beautiful. Here's all you've gotta do to acquire the trojan:
1. Surf to the porn site.
2. Pick the smut you'd like to see (OOPS! There's a message saying that your computer doesn't have the software necessary to show you "Sheep Hobbling For Randy Men" and offers to download and install said software for you).
3. At this point, you have a choice: If you must see "Sheep Hobbling For Randy Men" you can answer "HIT ME" and invite the delicious misery you've got coming or you can say "NO", go, and sin no more (at least 'til tomorrow).
4. If you've decided to download the codec that will allow you to consume all that sheepy goodness, you have to agree to the dialog that asks if you want to install the codec (there's a setting that skips this step if you're using the Safari web browser--you don't have to bother setting it, though. Live on the edge!)
5. Finally, supply the trojan with your administrative password. Really. Go ahead. Let me hear you go BAAA!, Mr. Sheep!
Congratulations. Your Mac is infected. The road to salvation can be found here.
Also, Salon Magazine's technology writer, Farhad Manjoo, has an excellent column on the advantages of buying a Mac.