Although it seems like the prolifer

Although it seems like the proliferation of spam—junk E-mails sent unsolicited to millions of people each day—is a recent problem, spam has been around as long as the Internet has. In fact, the first documented case of spam occurred in 1978, when a computer company sent out 400 E-mails via the Arpanet, the precursor to the modern Internet. Now spam E-mails account for more than two-thirds of all the E-mail sent over the Internet, and for some unlucky users, spam makes up 80 percent of the messages they receive. And despite technological innovations such as spam filters and even new legislation designed to combat spam, the problem will not go away easily.
The reason spammers (the people who and businesses that spread spam) are difficult to stop is that spam is so cost effective. It costs a spammer roughly one-hundredth of a cent to send spam, which means that a spammer can still make a profit even with an abysmally low response rate, as low as one sale per 100,000 E-mails sent. This low rate gives spammers a tremendous incentive to continue sending out millions and millions of E-mails, even if the average person never purchases anything from them. With so much at stake, spammers have gone to great lengths to avoid or defeat spam blockers and filters.
Most spam filters rely on a fairly primitive "fingerprinting" system. In this system, a program analyzes several typical spam messages and identifies common features in them. Any arriving E-mails that match these features are deleted. But the fingerprinting defense proves quite easy for spammers to defeat. To confuse the program, a spammer simply has to include a series of random characters or numbers. These additions to the spam message change its "fingerprint" and thus allow the spam to escape detection. And when programmers modify the fingerprint software to look for random strings of letters, spammers respond by including nonrandom content, such as sports scores or stock prices, which again defeats the system.
A second possible solution takes advantage of a computer's limited learning abilities. So-called "smart filters" use complex algorithms, which allow them to recognize new versions of spam messages. These filters may be initially fooled by random characters or bogus content, but they soon learn to identify these features. Unfortunately, spammers have learned how to avoid these smart filters as well. The smart filter functions by looking for words and phrases that are normally used in a spam message, but spammers have learned to hide words and phrases by using numbers or other characters to stand in for letters. For example, the word "money" might appear with a zero replacing the letter "o." Alternatively, spammers send their messages in the form of a picture or graphic, which cannot be scanned in the same way a message can.
Another spam stopper uses a proof system. With this system, a user must first verify that he or she is a person before the E-mail is sent by solving a simple puzzle or answering a question. This system prevents automated spam systems from sending out mass E-mails since computers are often unable to pass the verification tests. With a proof system in place, spam no longer becomes cost effective because each E-mail would have to be individually verified by a person before it could be sent. So far, spammers have been unable to defeat proof systems, but most E-mail users are reluctant to adopt these systems because they make sending E-mails inconvenient.
A similar problem prevents another effective spam blocker from widespread use. This system involves charging a minimal fee for each E-mail sent. The fee, set at one penny, would appear as an electronic check included with the E-mail. Users can choose to waive the fee if the E-mail is from a legitimate source; however, users can collect the fee from a spammer. A fee system would most likely eliminate a great deal of spam, but unfortunately many users find such a system too intrusive and inconvenient.
In some ways, the battles being fought over intrusive E-mails are very much an arms race. Computer engineers will continue to devise new and more sophisticated ways of blocking spam, while spammers respond with innovations of their own. It is unfortunate that the casualties in this technological war will be average E-mail users.