SPAM, SPIM and SPIT:

Spam is flooding the Internet with many copies of the same message, in an attempt to force the message on people who would not otherwise choose to receive it. Most spam is commercial advertising, often for dubious products, get-rich-quick schemes, or quasi-legal services. Spam costs the sender very little to send -- most of the costs are paid for by the recipient or the carriers rather than by the sender.
SpIM is a term that has recently been coined to refer to spam sent via instant messenger programs, such as AOL Instant Messenger, MSN Messenger and ICQ. Someone who sends instant messenger spam (SPiM) is referred to as a spimmer, again a play on the term spammer.
SPIT (Spam over Internet Telephony) is one of the foreseen future forms of spamming that Internet authorities are preparing for today. With the increasing use and dependence on the Internet for communications and data transfer, malicious software programmers have taken advantage by creating VoIP bots with the ability to harvest data and advertise massively at a very small cost. These advertising methods include email spams, SPIMS or spams over instant messaging applications, malicious bots that generate pop up ads, initiate redirects, etc.