Backdoor is a software program that gives an attacker unauthorized access to a machine and the means for remotely controlling the machine without the user's knowledge.

后门是一个软件程序，使黑客未经授权访问的机器和手段，远程控制的机器在用户不知道。

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If you do open the file then your security software is disabled, a backdoor is installed and the worm will start trying to reach the people on your personal buddy list.

BBC: Hand on keyboard