Christian Haschek analyzed 443 free proxies before claiming only a mere 21% are “not shady” Of those, 33 proxy servers modified static HTML pages and injected ads. Seventeen of the 199 proxies modified JavaScript mostly to inject ads. Same risks apply to Tor exit nodes, according to BADONIONS project analysis. BadONIONS works like this: You download a list of all the Tor exit node from here and then you use the Stem API to connect to every exit node out there and login to a website.”]
Source: https://www.csoonline.com/article/2938914/shady-free-proxies-and-tor-exit-nodes.html