I have an SMS blocker Android application developed myself which was working quite well capturing all the spams until recently Google updated its Hangouts app to work with S
Hangouts uses the maximum possible priority (999 per the Intent-Filter docs) and therefore you cannot abort it on <4.4 releases. On 4.4+, only the default SMS app (blog post with details) can receive SMS notifications - users would need to set your app as the default SMS app for your app to function correctly (although it should function as expected if that happens).