Vampires are everyday citizens with everyday lives who simply have been overcome by a virus which gives them an insatiable desire for blood (much like die-hard crack addicts - see SFM Virus.). Vampires require fresh human blood to survive. This means the blood can't come from animals, other vampires, or blood banks.
No one is safe from their attacks - friends, relatives, co-workers, etc. Especially at risk of attack are victims who have already been bit - which they refer to as cattle. They give off a scent which incites vampires into a feeding frenzy. And much like sharks, vampires can smell The Hunted miles away.
A vampire takes only enough blood to quench his thirst. If the victim is drained of blood completely and dies, they also become a vampire. A vampire is not always aware that they have created another vampire. Much like alcoholics, they take as much as they can without worrying about the consequences.
Vampires all have different abilities and special powers. Superhuman strength and reflexes are a given. Some are also shape-shifters, others can turn into smoke, see in the dark, turn invisible, fly, walk through walls, read minds, control thoughts - especially those of the opposite sex through increased pheromone production. Vampires have regenerative powers which vary in speed depending on the strength of the vampire. In time, they can regrow entire limbs. Thus, bullets cannot harm them, though they can feel pain and it may slow them down a bit. Vampires are immortal and do not age after they have been turned.
Like cockroaches, Vampires have developed an immunity to practically everything over the years. They are sensitive to sunlight and typically wear dark glasses, but they do not explode in flames at the break of day. They do not fear crosses or holy water, they're just not avid church goers. They are not allergic to garlic but garlic pills can mask the scent and taint the blood of their prey. Silver bullets and a stake in the heart will only piss them off. Vampires can only be killed by removing their head from their body (with sword, axe, or any other means). Thus, many vampires have become skilled in the use of swords to protect themselves from their only true weakness. Vampires have an almost uncontrollable desire for blood, and can grow weak if they do not have fresh human blood to sustain them. If they do not get blood within a certain amount of time (which varies for each vampire), they will wither and die.
It is virtually impossible to recognize a vampire, unless their emotion or hunger flares, at which time their eyes may glow red and fangs will develop. They may also have two teeth marks visible on their neck from when they were first bit. They can be seen in mirrors and on film, although they always have the familiar "red eye" when taking flash photography. The only way to determine if someone is a vampire is to simply wait and see if they wither and die when deprived of blood, which may take an undetermined amount of time.