Sprint is now pushing the May security update to the HTC Arrive users. This update does not adds any new features but does fixes fraudulent security certificates. Interesting thing to note about this update is the fact that only operating system is updated while the radio is left untouched.
To perform the update, connect your Windows Phone to your computer and then go to settings > phone > update. Then, make it check for the update (7.0.7392.0).