A file integrity program such as Tripwire protects against Trojan horse attacks by:

A.
Using programming hooks to inform the kernel of Trojan horse behavior

B.
Rejecting packets generated by Trojan horse programs

C.
Helping you catch unexpected changes to a system utility file that might indicate it had been replaced by a Trojan horse

D.
Automatically deleting Trojan horse programs

Explanation:
Tripwire generates a database of the most common files and directories on your system. Once it is generated, you can then check the current state of your system against the original database and get a report of all the files that have been modified, deleted or added. This comes in handy if you allow other people access to your machine and even if you don’t, if someone else does get access, you’ll know if they tried to modify files such as /bin/login etc.