Theresa dual boots her iMac with Parallels, and is wondering if she needs to have a backup of each operating system separately. Leo says she does not, if she's running the other operating system in Parallels. If she was using Boot Camp to run each operating system natively on her Mac, then she would need to have separate backups. When she runs Windows in Parallels, it's actually running within OS X. That means, when OS X backs up, so does her installation of Windows.
She's also wondering about AntiVirus. Leo says that a virtual version of Windows is sandboxed, so if she did get a virus, she can just throw away the virtual install of Windows and start over. It won't harm the rest of her system.