Third-party APK sites are breeding grounds for malware. Hackers often take legitimate-looking apps like SMS Bomber PRO and inject them with:
Using this app to harass, bully, or cause distress to others is a violation of most terms of service and can have legal consequences. SMS Bomber PRO Apk Latest -v2.21- Download For Android
If you become a target of SMS bombers (someone used a tool like this against you): Third-party APK sites are breeding grounds for malware