Web protection service

I am looking to build software, which will among other things analyze files from the web and protect users from running them if they do not pass a security test. This project is only creating the part which filters all http/https urls in windows (both browsers and executable). For each URL that returns an executable (check http response for file-magic: MZ,PK and MSI magic) and save it to the file-system - call a dummy filtering function with the file-location and URL. Popup a message-box to the user for accept/deny access to the file in the file-system. Support: • Chrome ; Firefox ; IE8/9/10 and other downloadable files that fetch executable • Vista/Win7/8 ( XP is nice to have) ; Platforms : x32/x64 • No browser extensions and no use of AppInit_DLLs. Possible solutions Preferable solutions : User-Space only / no drivers / no CA certificates installation. 1. Global API Hooking ( need to support Firefox as well ) 2. WFP ( Windows Filtering Platform ) ; doesn't support XP 3. Specific API Hooking for top browsers and key software 4. Device driver / LSP ( need to support Firefox as well ) 5. Catch getaddrbyname/getaddrinfo, WSRecv/WSSend, CreateFile requests. Please only offer if you have significant experience in similar projects and can provide long term support the code. I'd like to discuss possible solutions with you and make sure we have covered all bases before defining the exact project scope.