Proxy Servers at their very core and function are never secure or anonymous. Remember that someone has chosen to run the proxy server and can see who you are, and that your data and passwords are not secure.
People wishing to remain anonymous through a proxy server are fooling themselves. The best solution is to use a VPN account because they are secure, and also make you anonymous.
Consider the dangers of so-called anonymous proxy servers before using them, and understand that you are more at risk in terms of security and anonymity when using a proxy server. VPN Accounts are the most frequent way that people find true anonymous surfing rather than using proxy servers.