Apple puts everything into a sandbox, so if you are un-jailbroken, you can forget about virus problems because they do not exist. If someone were to create an exploit that could create problems, it would be big news.
When you JB, however, you open iOS up to potential problems because now, iOS is open and exposed.
If you JB, you MUST change your root password. Unless it is changed, it is 'Alpine." Every iPad on the planet has exactly the SAME PASSWORD and that would be Alpine.
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