A trojan, or trojan horse, is a seemingly legitimate program which secretly performs other, usually malicious, functions. It is usually user-initiated and does not replicate.
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Trojan:SymbOS/Appdisabler.A is a malicious SIS file dropper, which is dropped by the Skulls.J trojan.
Appdisabler.A tries to disable third party file managers and drops two other malwares:
When installed, AppDisabler.A will replace many third-party file managers as well as other third party applications with non-functional application files. It also drops Locknut.B and Cabir.Y onto the system.
When active, Appdisabler.A disables following applications:
The dropped malware Cabir.Y will not start automatically, but will attempt to start at the next boot. However, on most devices Locknut.B will cause application loading to fail. This prevent Cabir.Y from starting.
Appdisabler.A also contains a bootstrap component that attempts to start a component of Skulls.J showing animation of flashing skull. This functionality is also hampered by Locknut.B.