SPAM in a system (e-mail) is

Correct — A, (a) A message distributed indiscriminately.

SPAM is UNSOLICITED BULK ELECTRONIC MAIL, and the definition has exactly two parts. Both are needed, and the option on the page names them together.

UNSOLICITED — the recipient never asked for it and has no prior relationship with the sender. A newsletter you subscribed to is not spam however often it arrives. BULK, sent INDISCRIMINATELY — the same message goes to an enormous list of addresses chosen without regard to who they belong to. A single unwanted message written to one person is a nuisance; spam is a mass operation.

The word 'indiscriminately' in the keyed option carries the second half precisely. Spam is not aimed; that is its defining economic feature. Sending an e-mail costs the sender essentially nothing, so a response rate of one in a million still pays, and the rational strategy is to send to everyone rather than to anyone in particular. Every other property of spam follows from that arithmetic — the volume, the harvested address lists, the use of networks of compromised machines to do the sending, and the forged sender addresses that make the source hard to trace.

WHY IT MATTERS BEYOND ANNOYANCE. Spam is the delivery vehicle for most e-mail-borne fraud and malware: PHISHING messages that imitate a bank or a service provider to harvest passwords, attachments and links that install malicious software, and advance-fee frauds. The cost falls on the receiving side — storage, bandwidth and filtering capacity — which is the reverse of ordinary advertising, where the advertiser pays.

HOW IT IS FOUGHT. By filtering at the mail server and the mailbox, using content analysis and statistical classification; by refusing mail from addresses and networks known to send it; by sender authentication schemes that let a receiving server check whether a message really came from the domain it claims; and by requiring positive opt-in before bulk mail may be sent at all.

The stem prints SPAM in full capitals and hyphenates 'e-mail' inside the parentheses, and it ends on 'is' with no punctuation, as this booklet's short definitional items do.

Why the others are wrong

• (b)A search engine — A different piece of internet machinery entirely. A search engine crawls the web, builds an index of what it finds, and returns ranked results when a user submits a query. The relationship with the user is the exact opposite of spam's: a search engine is a service you GO TO and ask, while spam ARRIVES without being asked for. The option is on the page as a category error rather than a near miss, and it is the kind of choice a candidate makes who recognises the word as 'something to do with the internet' without having a definition attached to it. Nothing in the stem's own wording — 'in a system (e-mail)' — is consistent with a search service.
• (c)An activity of the user — The most instructive of the three, because it gets the direction of the transaction backwards. Spam is defined by being UNSOLICITED: the whole point is that the recipient did nothing to invite it. If a user had asked for the message, requested the mailing or signed up for the list, it would not be spam at all, however commercial or frequent it might be. What the option describes is closer to a subscription. The person doing something here is the SENDER, and the recipient's role is entirely passive. The consent test is also how the law and the mail industry draw the line in practice, which is why bulk mailers are required to obtain positive opt-in and to offer a working way to unsubscribe.
• (d)A command initiated by the sender — Right about who acts and wrong about what the thing IS. Spam is a MESSAGE — content that travels through the mail system and is delivered to a mailbox. A command is an instruction to a program or a protocol, and mail transfer certainly has such commands: the Simple Mail Transfer Protocol exchanges verbs between the sending and receiving servers to open a session, declare the sender, declare each recipient and begin the message body. But those commands carry the mail; they are not the mail. Confusing the message with the protocol that moves it is a common shape of error in networking items, and it is worth fixing early, because several questions on this paper turn on keeping the content, the protocol and the device separate.

SPAM is unsolicited bulk electronic messaging. The two conditions are independent and both are required: a message the recipient did not ask for, sent in bulk to addresses gathered without regard to who holds them.

WHY IT EXISTS AT ALL is a matter of economics. The marginal cost of sending one more e-mail is near zero, so unlike print or broadcast advertising, spam does not have to be targeted to be profitable. A vanishingly small response rate still returns more than the sending costs. That single fact explains the entire phenomenon: the sheer volume, the harvesting and trading of address lists, the use of BOTNETS — networks of computers compromised by malware and used without their owners' knowledge — to spread the sending across thousands of machines, and the forging of sender addresses to frustrate blocking.

THE FAMILY OF RELATED TERMS, which option sets like to mix:

PHISHING — a message that impersonates a bank, employer or service provider to trick the recipient into surrendering passwords, card details or a payment. Delivered by spam, but defined by the deception. SPEAR PHISHING — the same deception aimed at one named individual using details specific to them, and therefore not indiscriminate at all. SPOOFING — forging the sender address or other identifying information so the message appears to come from someone else. MALWARE — malicious software, of which spam is a principal delivery route through attachments and links. HOAX and CHAIN MAIL — messages that recruit the recipient into forwarding them onward.

COUNTERMEASURES operate at several layers. Content FILTERING scores each message on its text, structure and links, using statistical classifiers trained on known spam and known good mail, and diverts what it judges unwanted to a junk folder. REPUTATION systems refuse or downgrade mail from network addresses and domains that are known sources. SENDER AUTHENTICATION lets a receiving server verify that a message genuinely originated from the domain in its address, which attacks the forgery that spam depends on. And regulation in many jurisdictions requires positive consent before bulk commercial mail may be sent, together with a working unsubscribe facility.

THE ASYMMETRY OF COST is what makes spam a policy problem rather than merely a nuisance. Nearly all the expense — bandwidth, storage, filtering infrastructure and the recipient's time — falls on the receiving side, while the sender pays almost nothing.

Key facts

• Spam is UNSOLICITED BULK e-mail: the recipient did not ask for it, and the same message is sent indiscriminately to very large numbers of addresses.
• Both conditions are needed — a mailing the recipient positively opted into is not spam, and a single unwanted message to one person is not bulk.
• The economics are the explanation: sending costs the sender almost nothing, so an extremely low response rate is still profitable and targeting is unnecessary.
• Nearly all the cost of spam — bandwidth, storage, filtering and the recipient's time — falls on the receiving side rather than the sender.
• Spam is the principal delivery route for phishing, advance-fee fraud and malware carried in attachments and links.
• Phishing is defined by IMPERSONATION of a trusted party to obtain credentials or payment; spoofing is the forging of the sender's identity; the two are distinct from spam itself.
• Bulk sending is often done through botnets — networks of computers compromised by malware and used without their owners' knowledge.
• Defences run at several layers: content filtering and statistical classification, reputation-based blocking, sender authentication that verifies the sending domain, and opt-in requirements with a working unsubscribe facility.

Common traps

• Defining spam by its content — advertising, or fraud — rather than by being unsolicited and sent in bulk. A legitimate advertisement to an opted-in list is not spam.
• Treating spam and phishing as the same thing. Phishing is defined by impersonation and credential theft; it is usually delivered by spam but is not identical with it.
• Placing the activity with the recipient. Spam is something done TO a user, and consent is exactly what distinguishes it from a subscription.
• Confusing the message with the protocol that transports it, which is what the 'command initiated by the sender' option is built on.
• Assuming that unsubscribing always works. It is required of legitimate bulk senders, but responding to genuine spam mainly confirms that the address is live.

• practice — not a real PYQ

  An e-mail that appears to come from a bank and asks the recipient to confirm account credentials on a look-alike website is an example of

  • (a)spooling
  • (b)phishing
  • (c)caching
  • (d)defragmentation

  Answer(b) phishing — the defining feature is IMPERSONATION of a trusted party in order to obtain credentials or a payment. Spooling is the queuing of jobs such as printing so that a slow device does not hold up the processor; caching keeps recently used data close at hand for speed; defragmentation reorganises files on a disk. None of the other three has anything to do with deception.

• practice — not a real PYQ

  Which one of the following protocols is used to SEND an e-mail message from a client to a mail server ?

  • (a)SMTP
  • (b)POP3
  • (c)IMAP
  • (d)FTP

  Answer(a) SMTP — the Simple Mail Transfer Protocol carries mail outward from a client to a server and onward between servers. POP3 and IMAP both work in the opposite direction, retrieving delivered mail into a client, the difference being that POP3 typically downloads and removes it while IMAP keeps it synchronised on the server. FTP transfers files and has no role in mail.