This is barely relevant to Mac malware, but it has a lot to do with security mechanisms that use numeric passcodes and PINs (personal identification numbers), which of course includes lots of mobile devices and iGadgets. Hearing a PIN drop is an article published in Virus Bulletin in September 2011.
Most research on patterns of password use is based on the analysis of known collections of exposed passwords to see which are the most commonly used. However, there are few (if any) publicly known repositories of known account/passcode pairs, and that has restricted equivalent research on numeric passcodes. This article presents preliminary findings from analysis of a data set of passcodes ordered by frequency of use, generously provided by Daniel Amitay. (I hope to present a more detailed analysis of passcode selection strategies in 2012: the research project is ongoing.)
David Harley CITP FBCS CISSP
Small Blue-Green World/AVIEN/Mac Virus