These answers, and many other on the forum, about the danger of PC viruses on Macs reassure me, but not completely. The Sophos AV program tells me that the Windows files on my iMAC are infected with the Bredo-Q malware, which it is unable to eliminate.
No Windows app, including malware, can run on Mac OS X. It cannot in any way affect your Mac OS X side; only the Windows installation.
Sophos should be avoided, as it could actually increase your Mac's vulnerability, as described
here and
here... and
here.
ClamXav is a better choice, since it isn't a resource hog, detects both Mac and Windows malware and doesn't run with elevated privileges.
You don't need any 3rd party antivirus app to keep your Mac malware-free. Macs are not immune to malware, but no true viruses exist in the wild that can run on Mac OS X, and there never have been any since it was released over 10 years ago. You cannot infect your Mac simply by visiting a website, unzipping a file, opening an email attachment or joining a network. The only malware in the wild that can affect Mac OS X is a handful of trojans, which cannot infect your Mac unless you actively install them, and they can be easily avoided with some basic education, common sense and care in what software you install. Also, Mac OS X Snow Leopard and Lion have
anti-malware protection built in, further reducing the need for 3rd party antivirus apps.
The operation of my MAC seemed fine, but recently my email account and password were hijacked by some thug in Nigeria. Is there any possible connection?
There is no connection. Your email accounts can be hacked, even if you don't own a computer. It has nothing to do with what computer or OS you're running. Change your email passwords to something complex, including numbers, special characters and upper and lower case letters.