Windows 2000's default permissions provide the Everyone group with Full access (Everyone:F) on the system root folder. In most cases, the system root is not in the search path. However, during logon or when applications are invoked directly from the Windows desktop via Start | Run - it can be.
This scenario could enable an attacker to mount a Trojan horse attack against other users of the same system, by creating a program in the system root with the same name as some commonly used program, then waiting for another user to subsequently log onto the system and invoke the program. The Trojan horse program would execute with the user's own privileges, thereby enabling it to take any action that the user could take.
For details on the required administrative procedure, click here.