Security Alert Phone Repair May Be Required

I keep receiving push notifications about a security alert. It says that I need to repair my iphone by visiting a URL and downloading the recommended security app. My question is: Is this legit? Is it from apple? How do I fix this? Also, if its not from apple is there any security measures I do need to take in order to keep something from happening. Lastly, How do I keep it from not alerting me all the time?