http://diggy.i2p/articles/botnet.xhtml
Of course, VPN traffic is also easily blocked at the ISP or website level. VoIP, social, IM, etc. Simply suffers from lack of usage - so if you want to actually reach anyone, it's Facebook, Skype, etc. Much of the commonly recommended "secure and private" IM software has various issues (Signal and Telegram require a phone number; Keybase has had a security audit which found many issues (local) ; Matrix protocol has just had...