In the name of Allah, the Most Gracious, the Most Merciful. Imam al-Nawawi's collection of 40 Hadiths is one of the most collections of hadiths we have today. Imam al Nawawi actually compiled a total of 42 hadiths for this collection, not 40. He was one of the greatest scholars of Islam and lived from 631 A. H. To 676 A. H, passing away at the age of 45.
Hadith Nawawi Bangla is completely safe to download. Apps for Bangladesh is the official developer of the tool that can be found in the Books & Reference category. The most recent update of the app was released on Mar 6, 2015 and this application has been installed by over 5K users.