How can I stop people I don't know from following me on twitter?

[michael s]

The goal of most people on twitter is to get as many followers as possible....then use those followers to send messages to if you have a website and use it for marketing purposes...I welcome new followers all the time...I have a Website but i have not used twitter to market that site because i don't want to be accused of SPAM...however now i have a automatic message telling people thanks for the follow and be sure to visit my website full of helpful tips to keep your computer working lightning fast and FREE products for them to look at and download....

Use your twitter account to your advantage...and don't get mad because you have people following you....that is a plus...if you know how to use twitter.....Many people including myself use it for business and personal reasons....I have 2 sites on Twitter...The first site is for FREE stuff for the computer and my other site is for business only.....they both do equally well.....

http://twitter.com/cfmike2010