Systems and methods for controlling the number of clients that can access a server in a server-client network are described. A communications filter driver resides on the server and monitors network communications to determine a unique network address of each client that attempts to access the server. A table of clients that have accessed the server is stored at the server. When a client attempts to access the server, the server allows the client to access the server if the network address of the client is listed in the table. If the network address of the client is not listed in the table, the server determines if a client limit has been met or exceeded. If the limit has not been met, the client is allowed to access the server and the Internet address of the client is added to the table.