Phishing is the practice of defrauding users into giving up their usernames, passwords, credit card numbers and other personal information. According to various estimates, about 80% of all email in the world may be spam. Much of it is sent by botnets, networks of virus-infected computers, complicating the process of tracking down the spammers. Spam is unsolicited junk email sent indiscriminately in bulk, often for commercial purposes.