"Swine Flu" strain is basically a genetic tossed salad of pig, bird and human flu virus.
So why is the pig part getting all the "glory"? According to Andrew Pekosz, over at the Johns Hopkins School of Public Health, it's because the two genes most important to determining whether humans are immune and what level of protection they have (that'd be the "H" and the "N" in H1N1, by the way) happen to be ones that came from porcine flu strains. We call this chimera "Swine Flu" because that's where it got the genes that really matter most to our health.
Source(s):
http://www.boingboing.net/2009/04/27/swine-flu-fun-facts.html

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It is believed to have originated in pigs and spread directly from pigs to humans. There are several strains of swine flu, but this one appears to be brand new. Hence it is not really "the" swine flu but just another strain of the H1N1 virus that has been around for decades.
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What is Swine Influenza?
Swine Influenza (swine flu) is a respiratory disease of pigs caused by type A influenza virus that regularly causes outbreaks of influenza in pigs. Swine flu viruses cause high levels of illness and low death rates in pigs. Swine influenza viruses may circulate among swine throughout the year, but most outbreaks occur during the late fall and winter months similar to outbreaks in humans. The classical swine flu virus (an influenza type A H1N1 virus) was first isolated from a pig in 1930.
Source(s):
http://www.cdc.gov/swineflu/key_facts.htm

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Swine influenza, or “swine flu”, is a highly contagious acute respiratory disease of pigs, caused by one of several swine influenza A viruses. Morbidity tends to be high and mortality low (1-4%). The virus is spread among pigs by aerosols, direct and indirect contact, and asymptomatic carrier pigs. Outbreaks in pigs occur year round, with an increased incidence in the autumn and winter in temperate zones. Many countries routinely vaccinate swine populations against swine influenza.

Swine influenza viruses are most commonly of the H1N1 subtype, but other subtypes are also circulating in pigs (e.g., H1N2, H3N1, H3N2). Pigs can also be infected with avian influenza viruses and human seasonal influenza viruses as well as swine influenza viruses. The H3N2 swine virus was thought to have been originally introduced into pigs by humans. Sometimes pigs can be infected with more than one virus type at a time, which can allow the genes from these viruses to mix. This can result in an influenza virus containing genes from a number of sources, called a "reassortant" virus. Although swine influenza viruses are normally species specific and only infect pigs, they do sometimes cross the species barrier to cause disease in humans.

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Source(s):
http://www.who.int/csr/disease/swineflu/faq/en/index.html

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