to access their own BBS without having to wait for a user to log off and/or be rude and kick them off. One other side-effect of the multi-line capability was that IBM's OS/2—specifically the Warp version—became a popular choice for some WWIV sysops, as the default two instance configuration could easily run under the most basic OS/2 system with ease. In the BBS world, WWIV was referred to sometimes as the "only killer app for OS/2, and it wasn't even written for it!". WWIV did run well even in Microsoft Windows, though—often better than Windows-native BBSs—because DOS applications ran preemptively, even with Windows 3.1. WWIV also ran well under Quarterdesk's DESQview and DESQVIEW/X multitasking shells. The switch to C also allowed for Bell to implement a rather flexible BBS network, WWIVnet, allowing all WWIV boards to link to each other. Bell also took the opportunity to try to make some small amount of money back for his efforts. Starting with the C version, those who paid a registration fee, as high as $80 in 1994, received copies of the source code to modify and recompile. The ability to modify WWIV as a sysop saw fit was one of its selling points—something that RBBS, Opus, Genesis, and many of the other BBS programs of the era refused to provide, usually on the basis of the perceived security risk. Nevertheless, source code availability was not lost on the thousands of WWIV sysops, who had begun to regard Bell as a cross between a father figure and a revolutionary. Registration also was required for membership in WWIVnet, which encouraged the growth of alternative WWIV-based networks. This also generated a subculture of unregistered WWIV boards, which at its peak represented a multiple of the number of officially registered boards, and even passed around unlicensed copies of the source code, as well as forming their own networks. The rise of WWIVnet Registration also provided permission to link to the main network, WWIVnet, which soon connected thousands of boards together into a network spread across several nations. Boards in a WWIV network are identified within the network by a node number. Local e-mail within a board was sent by sending a message to a BBS user's user number (the sysop always being user 1). However, to e-mail a user at another board within a WWIV network, the @ sign would be added (similar to an internet