五、閱讀測驗 10 %     Although it seems like the proliferation of spam—junk E-mails sent unsolicitedto millions of people each day—is a recent problem, spam has been around as long asthe Internet has. In fact, the first documented case of spam occurred in 1978, when acomputer company sent out 400 E-mails via the Arpanet, the precursor to the modernInternet. Now, Spam E-mails account for more than two-thirds of all the E-mail sentover the Internet, and for some unlucky users, spam makes up 80 percent of themessages they receive. And, despite technological innovations such as spam filters,the problem will not go away easily.     Most spam filters rely on a fairly primitive “fingerprinting” system. In thissystem, a program analyzes several typical spam messages and identifies commonfeatures in them. Any arriving E-mails that match these features are deleted. But thefingerprinting defense proves quite easy for spammers to defeat. To confuse theprogram, 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 spamto escape detection.     A second possible solution takes advantage of a computer’s limited learningabilities. So-called “smart-filters” use complex algorithms, which allow them torecognize new versions of spam messages. These filters may be initially fooled byrandom characters or bogus content, but they soon learn to identify these features.Unfortunately, spammers have learned how to avoid these smart filters as well. Thesmart filter functions by looking for words and phrases that are normally used in aspam message, but spammers have learned to hide words and phrases by usingnumbers 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 theirmessages in the form of a picture or graphic, which cannot be scanned in the sameway a message can.     In some ways, the battles being fought over intrusive E-mails are very much anarm race. Computer engineers will continue to devise new and more sophisticatedways of blocking spam, while spammers will respond with innovations of their own.It is unfortunate that the casualties in this technological war will be average E-mailusers.
76. The author describes spam as _____.
(A) a recent problem that affects millions of users
(B) totaling more than 80 percent of E-mails sent via the Internet
(C) a technological innovation
(D) unwanted messages sent to a mass audience