I'd have them manually back up any photos, contacts or personal documents on there, and then do a factory reset of the phone, re-downloading the apps from the app store or having them side loaded via *.apk files. If its a carrier "feature" this will not take care of the issue. but if it's an app with to many permissions forwarding info, it will obviously kill it. Since the cause isn't known, can't really say that an anti-virus/trojan would fix the problem. When you can't tell the issue, nuke the device clean and start at square one. It's a bit annoying, but the safest course outside of buying a new device.