Lecture 31, filtering out spam. After studying this chapter you will be able to understand: Spam and computer security; how i read my email; the acronyms MTA, MSA, MDA, MUA, etc; structure of email messages; how spammers alter email headers; a very brief introduction to regular expressions; an overview of procmail based spam filtering; writing procmail recipes. | Lecture 31: Filtering Out Spam Lecture Notes on “Computer and Network Security” by Avi Kak (kak@) April 12, 2016 2:50pm c 2016 Avinash Kak, Purdue University Goals: • Spam and computer security • How I read my email • The acronyms MTA, MSA, MDA, MUA, etc. • Structure of email messages • How spammers alter email headers • A very brief introduction to regular expressions • An overview of procmail based spam filtering • Writing Procmail recipes Computer and Network Security by Avi Kak Lecture 31 CONTENTS Section Title Page Spam and Computer Security 3 How I Read My Email 5 Structure of an Email Message 13 How Spammers Alter the Email Headers — A Case Study 20 A Very Brief Introduction to Regular Expressions 24 Using Procmail for Spam Filtering 43 Homework Problems 62 2 Computer and Network Security by Avi Kak Lecture 31 : SPAM AND COMPUTER SECURITY • Spam is a major source of malware that infects individual computers and, sometimes, entire networks. • Much spam tries to lure you into clicking on URLs of websites that serve as hosts for viruses, worms, and trojans. Consequences of inadvertently downloading such software into your computer can be deadly — as previously described in Lecture 30. • In addition to the dangerous spam that may try to steal information from your computer or turn it into a spambot for spreading even more spam, there is also another kind of spam these days: This consists of email generated by legitimate businesses and organizations that you either have no interest in reading or have no time for following up on. [For example, half of my spam consists of unsolicited messages sent to me by marketing companies, public relations houses, government agencies, university departments advertising their activities, and students in various parts of the world seeking to come to Purdue. Even just opening all of these messages would consume a significant portion of each day. ] • I am
