[onion2k]

Something to note about this strategy is that older versions of IE (10 and older) only support TLS 1.0 by default. Below 8 you're stuck with TLS 1.0 and can't even enable anything higher. So if "https://www.cdc.gov" is using modern web security IE users won't even get to request data from the server, so you can't detect their browser.

[user5994461]

To add more info. TLS 1.0 is prohibited from usage by many regulations and it will be immediately flagged by any security audit/tools. The government contract most certainly includes clauses about security and following recommended practices.

In short, anything below IE 11 is de-facto out of the picture.