1. A method for modifying intercepted data, the method comprising: receiving, at a security application executing in a security data processing system from an intercepting agent executing in an intercepting data processing system, an intercepted packet of data arranged according to a protocol; applying a security policy to the intercepted packet; encoding, using a processor and a memory at the security data processing system, in an instruction according to a coding grammar, a modification of the intercepted packet, wherein the instruction is suited for the encoding under a circumstance of the modifying; and sending the instruction to the intercepting agent, wherein the intercepting agent at the intercepting data processing system performs the modification according to the security policy and independently of the protocol.