1. A gateway computer for protecting a client computer against dynamically generated malicious content, the gateway computer comprising: a receiver configured to receive original content, the original content comprising a call to an original function, the call including an associated input; a content modifier unit configured to modify the original content to produce modified content, wherein the modified content includes a call to the original function and a call to a shielding function, the shielding function being operable to cause the client computer to transmit an instruction to a security computer to inspect the input associated with the call to the original function; and a transmitter configured to transmit the original content to the security computer and to transmit the modified content to the client computer, thereby allowing, based on the original content, detection of dynamically generated malicious content.