Spammers have been harvesting email addresses from the Internet for as long as I can remember. They have used different tools such as viruses, worms and scripts that crawl the web. The latest tool that has been developed uses a real-time program that provides the spammers with fresh email addresses that are gathered almost as quickly as they are posted.
According to an article posted by Dancho Danchev at ZDnet, this new tool queries Twitter for common phrases like "contact me at", "send me an email at", or "email me at" to find the email addresses. When it finds a new email address, it is sent to the spammer and indexed into a database that can be sold to other spammers worldwide.
As more and more people use Twitter to build contacts with people around the Internet, they are also feeding the spammer's database with new and valid email addresses. So be careful when tweeting and be aware that the bad guys are also watching what you tweet.