Described herein is a method and system for prevention of personal computing attacks, such as JavaScript Objection Notation (JSON) attacks. An intermediary device is deployed between a plurality of clients and servers. A firewall executes on the intermediary device. A client sends a request to the server and the server sends a response to the request. The intermediary device intercepts the response and identifies that the response may contain possibly harmful content. The application firewall parses the content of the response and determines whether it contains any harmful content. If it does, the application firewall blocks the response from being sent to its destination. Additionally, the method and system can provide other security checks, such as content hijacking protection and data validation.