You may have just accidentally clicked on an ad. I know I've done that every now and again.
No, it generally takes you to the marketplace where you would have to confirm if you want to purchase. I have a hard time believing it's a virus.
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I'm curious if someone hacked your account on the web and sent those apps to your phone?
I don't want to know your password, but is it something short that might be easy to hack? And/or is your xblive password the same one you use to access the email account you used to log into your xbl account? You should have those passwords separate
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So clicking on an ad can download something like an application from store?