[unboggling]

Regarding security on computer, I wouldn't want to risk running without comprehensive and frequently-updating antivirus and anti-spyware protection. I use that along with an OS X based firewall, behind good security on my wireless router. There are security threats aimed at OS X, though there seem to be less of them than for Windows.

With Dropbox (or equivalent), the files that reside in the Dropbox folder on my computer have been virus scanned, so syncing to the file hosting/syncing server and mobile devices doesn't offend my sense of security.

iOS devices are different, but with those I try to funnel most email and downloads through the computer (and its protection) before transferring to device. To me that's safe. I don't have to trust security precautions of outside companies or servers, or even Apple's walls between apps on iOS devices. I make exceptions sometimes, doing email with attachments or downloads direct to devices, but I keep in mind that doing so is less safe. I also try to limit surfing on iOS devices to known safe sites.

Even if there is not yet any malware that affects iOS devices directly -- which I don't know is true -- that doesn't mean iOS devices cannot be the recipients and transmitters of malware back to the computer, Windows or OS X, bypassing firewalls on the computer and local network.