LeechModem was a

BBS BBS may refer to: Ammunition * BBs, BB gun metal bullets * BBs, airsoft gun plastic pellets Computing and gaming * Bulletin board system, a computer server users dial into via dial-up or telnet; precursor to the Internet * BIOS Boot Specificat ...

file transfer protocol The File Transfer Protocol (FTP) is a standard communication protocol used for the transfer of computer files from a server to a client on a computer network. FTP is built on a client–server model architecture using separate control and data ...

client. LeechModem was compatible with protocols like XMODEM (and

YMODEM YMODEM is a file transfer protocol used between microcomputers connected together using modems. It was primarily used to transfer files to and from bulletin board systems. YMODEM was developed by Chuck Forsberg as an expansion of XMODEM and was ...

), but it would mischievously

NAK In data networking, telecommunications, and computer buses, an acknowledgment (ACK) is a signal that is passed between communicating processes, computers, or devices to signify acknowledgment, or receipt of message, as part of a communicatio ...

the last packet and then abort the file transfer. The user had successfully downloaded the file, but the BBS would mistakenly not count the aborted file transfer against the user's download quota. The user would need to know and input the filesize before the transfer so the client would know when to abort. Leech-modem was designed by Sam Brown. Leech

ZMODEM ZMODEM is an inline file transfer protocol developed by Chuck Forsberg in 1986, in a project funded by Telenet in order to improve file transfers on their X.25 network. In addition to dramatically improved performance compared to older protocol ...

was suggested by Sam Brown but written by a long lost friend in Atlanta, GA. Leech

was a LeechModem variant that was compatible with the faster

streaming file-transfer protocol. Subsequent versions of Leech

were authored by Sam Brown. LeechModem was used successfully for 2-3 years by a small group of people centered in the 408 area code and 203 area code. It was not until the LeechModem software was leaked that it was discovered and counter-measures were built into

software. Emulex/2 was the first BBS software to support Anti-LeechModem technology. This was because Sam Brown wrote Emulex/2

software as well. A common method was rounding the file size to the nearest kilobyte, causing the user to be unaware of the exact file size, rendering Leechmodem unusable.

See also