This indicates that an Android system on your network is infected by the Trojan FBILocker.
FBILocker is a piece of ransomware targeting Android mobile phones.
Any unprotected Android mobile phone is vulnerable to the attack.
System Compromise: Remote attackers can gain control of vulnerable systems
The signature can be set to "Block" to block the trojan's communication.
Use Anti-Virus software to scan and clean the system.