Hostile proxy and Open proxy

Hostile proxy:
Proxies can also be installed by online criminals, in order to eavesdrop upon the dataflow between the client machine and the web.All accessed pages, as well as all forms submitted, can be captured and analyzed by the proxy operator.For this reason, passwords to online services (such as webmail and banking) should be changed if an unauthorized proxy is detected

Open proxy server:
proxies might be used for abuse, system administrators have developed a number of ways to refuse service to open proxies. Many IRC networks automatically test client systems for known types of open proxy.Likewise, an email server may be configured to automatically test e-mail senders for open proxies .