A pubstro is a computer that has been cracked into, and had an FTP

File Transfer Protocol

File Transfer Protocol is a standard network protocol used to transfer files from one host to another host over a TCP-based network, such as the Internet. FTP is built on a client-server architecture and utilizes separate control and data connections between the client and server...

 server installed. This FTP server is used to facilitate the transferring and spreading of warez

Warez

Warez refers primarily to copyrighted works distributed without fees or royalties, and may be traded, in general violation of copyright law. The term generally refers to unauthorized releases by organized groups, as opposed to file sharing between friends or large groups of people with similar...

, or copyrighted software.

This is typically accomplished by scanning broad IP address

IP address

An Internet Protocol address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing...

 ranges with port scanner

Port scanner

A port scanner is a software application designed to probe a server or host for open ports. This is often used by administrators to verify security policies of their networks and by attackers to identify running services on a host with the view to compromise it.A port scan or portscan is "An attack...

s in search of servers running open ports that are vulnerable to attack by various scripts (e.g. CGI

Common Gateway Interface

The Common Gateway Interface is a standard method for web servers software to delegate the generation of web pages to executable files...

, PHP

PHP

PHP is a general-purpose server-side scripting language originally designed for web development to produce dynamic web pages. For this purpose, PHP code is embedded into the HTML source document and interpreted by a web server with a PHP processor module, which generates the web page document...

, VNC

Virtual Network Computing

In computing, Virtual Network Computing is a graphical desktop sharing system that uses the RFB protocol to remotely control another computer...

, etc.). The scripts are utilized to gain entry into the server whereupon the cracker uploads server software and creates logins. Many crackers will then patch the server against the very vulnerabilities they utilized to compromise the system thereby protecting it from being hijacked by other FXP

File eXchange Protocol

File eXchange Protocol and is a method of data transfer which uses FTP to transfer data from one remote server to another without routing this data through the client's connection. Conventional FTP involves a single server and a single client; all data transmission is done between these two...

 groups.

Although widely used among FXP board

FXP Board

An FXP board is an internet forum composed of members which distribute access to FTP servers or "pubstros". These forums are used to provide access to servers usually containing warez...

s, pubstros are frowned upon in the warez scene.