Making a ton of assumptions on your situation, here is how I would go about it. Record the IP addresses of your users (multiple per user), link these to user p

Making a ton of assumptions on your situation, here is how I would go about it. Record the IP addresses of your users (multiple per user), link these to user profiles and do a whois for each IP address. Big companies like the ones you mention will sometime appear to have their own IP address and you can then deduct the employer of your users. Additionally and assuming you have your users full names and email addresses, you can scrape the web and get their professional profile. Alternatively, you can probably buy some kind of user data but I would not know where to start except by googling around. All this can be build in a nice administrative UI for your application, from which good old human investigation can lead you to the specific people you are looking for to manually validate each user's employer.