Tonight, on Black Friday, several media sources noted that companies (selling in major box stores) that don't have their own smart phone apps are likely to find that crooks will create phony apps in their name.
The advice is to download the app from the vendor or possibly the retailer but not from an app store.
Another risk is that individuals who do not sign up for a particular service may learn that others have created accounts in their name. This could happen with Snapchat and Instagram. When I signed up for Instagram, I found a bogus account in my name with nothing in it, but it had to be removed first.