SymbOS/Unlock.A is the detection for a riskware application, usually named THC-NOKIA-UNLOCK.MDL that resets the Phone Lock of a device.  

The Phone Lock prevents the phone’s data from being accessed if the phone is stolen. It prevents a new SIM from being used on the phone and locks the keypad, Bluetooth, and USB ports as well. SymbOS/Unlock.A is a proof of concept tool that proves that this protection can be broken. The entire process of installing this on a device and breaking the Phone Lock has to be manually done. 

Manual Disinfection 

Scan your mobile device using UMU Scan and delete all files detected as SymbOS/Unlock.A.