but these days the uptake of users of Apple's products have made them mainstream and the hackers have taken notice.
They have taken notice.... but given the backend of OS X is BSD, their options are more limited than in the Microsoft world. Never say never, of course.... and same rules apply about not clicking on stuff etc.
Most of the exploits for OS X to date have taken place not on OS X directly, but through third-party software (e.g. Adobe Flash). So the old adage of keeping software up to date and only using software from trusted developers applies.
I concur with SHJ though on recommending Apple products.
As for gemma's original question.... might have been Wifi, maybe he's got a keylogger on his PC .... maybe he used someone else's computer to do his online banking at some point ? The possibilities are endless