Bifrost (Trojan horse)
Bifrost is a backdoor trojan horse family of more than 10 variants which can infect Windows 95 through Windows 10 (although on modern Windows systems, after Windows XP, its functionality is limited). Bifrost uses the typical server, server builder, and client backdoor program configuration to allow a remote attacker, who uses the client, to execute arbitrary code on the compromised machine (which runs the server whose behavior can be controlled by the server editor). The server component (sized around 20–50 kilobytes, depending on variant) is dropped to C:\Program Files\Bifrost\server.exe with default settings and, when running, connects to  a predefined IP address on TCP port 81, awaiting commands from the remote user who uses the client component. However, both installation directory and TCP port can be changed. TCP connection is encrypted with a password (default: "pass"), but this can be changed as well. It can be assumed that once all three components are operational, the remote user can execute arbitrary code at will on the compromised machine. The server components can also be dropped to C:\Windows and file attributes changed to "Read Only" and "Hidden". Casual users may not see the directories by default due to the "hidden