A computer system includes a host environment for the server, equipped with a port for communicating over an extended network and a network server to which is assigned a first network address or URL pathway. The computer system includes server applications and an access manager capable of receiving a call expression from the port. A call expression is a request from a user that includes the first network address or URL pathway. The access manager includes a discriminator that can be activated to check whether a call expression comprises a second URL-type segment that is different from the first network address or URL pathway; and a shunting device which activates the discriminator when the call expression is received from a registered user and if the discriminator determines that a call expression contains a second URL-type segment different from the first network address or URL pathway the shunting device activates a predefined application that isolates or rewrites the second URL-type segment.