'They're already here ...' reads the poster for Steven Spielberg's latest sci-fi thriller, War of the Worlds. The movie is about a massive alien attack. According to ufology researcher and screenwriter Jason Lam, aka Kee To, there is a good chance that it could happen. 'Our planet is unguarded, and many extraterrestrial life forms constantly travel to and from Earth,' said Lam, a committee member of the Hong Kong UFO Club. Lam said we are not aware of their visits because extraterrestrial life forms often do not have a visible body. He cited the fact that many gods documented in historical or religious texts appeared in a form of light. 'They may be a type of light energy or consciousness. As long as they can think, approach people, and have motives for their actions, we consider them a life form.' Many of these life forms are benign. But some may be irritable - just like the ones who destroyed the city of Sodom in the Bible, said Lam. In Genesis, Sodom is besieged by 'brimstone and fire from the Lord out of heaven', destroying the citizens and everything 'that grew upon the ground'. Lot's wife even becomes a pillar of salt when she looks back at the besieged city as she flees. 'Where did the fire from heaven come from?' said Lam. 'It might have been from a super-intelligent extraterrestrial civilisation that believed people in Sodom were evil and therefore wanted to disrupt the development of the city.' So why are some fictional aliens so keen on punishing humans? One common theory in ufology is that the early human race was in kinship with them. There is a huge chunk of the human genome - or genetic material - that is unused by the body, yet indispensable. It is often referred to as 'junk DNA'. Some ufologists argue that junk DNA stores locked knowledge and memories of the past that, if unleashed, would give people great powers. 'There are theories that say humans are life forms developed by aliens, who created them from their own DNA. But during the process, they deleted some powers and memories that they thought would be unbearable or inappropriate for living beings on this planet,' said Lam. These theories make wonderful material for a sci-fi novel, but are they backed up by science? Not according to scientist Tso Wung-wai, an adjunct professor at Chinese University of Hong Kong. As the convenor of the Study Group of Unexplained Phenomena, Professor Tso opposes claims that there have ever been alien visits. 'I can't use science to examine something developed from a parable or myth,' he said. 'People may have witnessed something extraordinary in the sky during the dawn of civilisation. But so what? Their observation may be biased, and I can't find any relevance between extraterrestrial life and these events.' Professor Tso added it would be too rash to conclude that our ancestors were created from extraterrestrial beings simply based on the mysteries surrounding junk DNA. 'We have unused sequences in our DNA, but they don't necessarily come from aliens. They could have been made redundant [during the process of evolution]. We scientists work by exploring every single piece of evidence and recording each step.' But no matter which side you are on, the question of whether the whole human race will eventually be wiped out by superior beings - be they extraterrestrial life forms or gods - will continue to haunt our imagination. 'Humans always need [fictional] enemies because it is through them that we build up solidarity within our societies and families,' said Lawrence Pun Kwok-ling, a writer on culture and movies and part-time university lecturer. 'And there are always the fears of being kept under surveillance or not being the superior being on this planet. That's why we are bewitched by dinosaurs, as they relate to our fears of extermination.'