If you use Pidgin, and you are getting SPAM from automated bots, Bot Sentry (link below) is an easy way to stop the SPAM. It works on Windows, Mac, and various flavors of Linux. Once you set it up, people who try to message you who are not on your contact list have to answer a question (like a Captcha) before their message is sent. The questions are really simple, so real people can still message you even if they don't know. But the question will stop automated bots from getting SPAM to you.