 Any received Message that is unwanted by the Recipient.
 Unsolicitated Commercial Email (UCE) or defined as “Unwanted”, “inappropriate” and “no longer wanted” Email.
 Real spam is generally e-mail advertising for some product sent to a mailing list or newsgroup.

Spam as a problem and ways to counter problems:
Spam may be defined as a problem due to following main Reasons described as under:
 Cost Shifting :
Sending bulk e-mail is amazingly cheap. With just a modem and a computer, spammers can send hundreds or thousands of messages per hour, and though that relatively minuscule cost of entry into the market is a potential advertiser’s dream, it quickly becomes a nightmare for those who pay the costs of receiving it.   If the costs were as minimal as the energy expended in pressing one button, spam would not be a concern.
 Fraud :

In survey after survey, the overwhelming majority of Internet users dislike receiving spam. In response to such strong consumer opinion, many ISPs have taken a variety of costly steps to reduce the volume of spam transmitted through their systems, including the buildup of extra capacity to accommodate the demands of filtering and storing what represents, according to America Online, nearly 30 percent of its daily mail traffic. Knowing that ISPs have taken those measures, senders of junk e-mail use tricks to disguise the origin of their messages. One of the most common is to relay their messages off the mail server of a third party. This tactic doubles the damages, because now both the receiving system and the innocent relay system are flooded with junk e-mail. For mail that gets through, many times the flood of complaints goes back to the innocent site because that site was made to look like the origin of the spam. Another common trick is to forge the headers of messages, making it appear as though the message originated elsewhere and again providing a convenient target upon which the anger of...