Yep. The Flashback Trojan... but hardly the first.
http://nakedsecurity.sophos.com/2010/11/24/apple-mac-malware-short-history/
The only reason fewer viruses are tailored to iOS is because there are fewer users (except tablets), and the animus targeted at MS.
As more Macs get sold, they will be more targeted since the idea that iOS is somehow more secure than Windows is completely erroneous.
edit: Speedy fingers, Wiz!