Four days ago Malaysia Airlines Flight 370 disappeared over the sea between Malaysia and Vietnam. The Beijing-bound flight that was carrying 239 people has yet to be recovered.

The Boeing 777-200ER took off from Kuala Lumpur, Malaysia, at 12:41 a.m. Two minutes later, the flight shows up on radar for the first time. At 1:20 a.m., air traffic control and radar lost contact with the aircraft. The last signal showed the plane at 35,000 feet about 140 miles off the coast of Vietnam.

Investigators are still searching for clues surrounding how the plane lost contact with air traffic control, who was involved and what caused it to disappear from radar screens in Southeast Asia.

So far, the investigation has revealed that two passengers used stolen passports to get on the flight. Using CCTV footage, the two men were identified as Pouria Nour Mohammad Mehrdad and Delavar Seyedmohammaderza – both from Iran. While this raised questions over a possible terrorist connection, investigators say the two men were most likely trying to seek asylum in Germany.

At least nine countries have begun to search for the plane or any evidence of it. The possible area where debris could be has been expanded to 100 nautical miles around the west coast of Malaysia. Vietnamese military planes saw two oil slicks in the water but both are believed to be caused by cargo ships, not an aircraft.

The plane’s mysterious disappearance has led to a plethora of conspiracy theories to explain what happened to the Malaysian Airlines flight. From the somewhat logical to the absurdly outrageous, below are the top five conspiracy theories the Internet has to offer:

1. Terrorist Attack

Some theorists have proposed Flight 370 was hijacked by terrorists. At first, this stemmed from the news surrounding the two stolen passports. The two men traveling with the stolen documents have not been linked to any terrorist organization. Investigators believe they were headed to Germany to seek asylum.

“We believe he is not likely to be a member of any terrorist group,” Malaysian police chief Khalid Abu Bakar said at a press conference.

Another terrorist-inspired theory involves the plane being hijacked and rerouted to an abandoned airport in Vietnam, where its radio devices have been turned off. Theorists make the case the plane will later be used as a ‘weapon of mass destruction’ with passengers and crew now being held as hostages.

Believers say a report from Chinese media supports this theory. The news agency says family members of those missing on the flight have called their cell phones which have rung, with no one picking up.

According to Jeff Kagan, a technology industry analyst, this is not necessarily a sign the 239 passengers are alive.

"When a customer calls another number," he told NPR, "the carrier has to decide what to do next."

While the phone carrier is searching for the phone being called, it lets the initiator of the call hear several rings before the two are connected. If the phone cannot be found the carrier can either drop the call, redirect it to the person’s voicemail or to a message saying the call could not be completed.

The Chinese Martyrs Brigade, a terror group, claimed responsibility for the attack. Members sent an email to Chinese journalists saying, “You kill one of our clan, we will kill 100 of you as pay back.”

Officials have discounted the claim calling it a hoax.

“There is no sound or credible grounds to justify their claims,” Malaysian Defense Minister Hishamuddin Hussein said.

2. Electronic Weaponry Onboard

Some have looked at the plane’s passenger list for clues. Analysis of the flight manifest revealed that 20 passengers worked for the same company: Freescale Semiconductor – a company that manufactures semiconductor chips. Twelve employees onboard came from Malaysia while the remaining eight are from China, according to the company’s spokesperson Jacey Zuniga.

Theorists say Freescale Semiconductor employees onboard may have used embedded processors to jam radar and other electronics to make the plane invisible for air traffic control.

3. Mechanical Error

Some have suggested the plane had a mechanical error or malfunction that made the aircraft explode midair.

"The fact that we are unable to find any debris so far appears to indicate that the aircraft is likely to have disintegrated at around 35,000 feet (10,600 meters),” a source involved in the investigations in Malaysia said.

So far, recovery efforts have yet to find evidence of a crash. Some theorists have proposed that if the plane did not explode, pilots may have been forced to ditch the plane in the water. But, if that were the case, there would have been an emergency signal sent much like the “miracle on the Hudson.” Malaysian and Vietnamese authorities did not receive a mayday call – which for the most part is possible except for a rare sudden emergency when it wouldn’t be possible to send one.

Dr. Eric Wong Tsun-tat of Polytechnic University told the South China Morning Post that an emergency signal takes 10 seconds to send.

"Even under very urgent circumstances, a pilot or the co-pilot will still have the chance to issue one to air traffic controllers, or to their own company," Wong, a former engineer at the Hong Kong Civil Aviation Department, said. Even if the pilots were unable to send a signal over the radio, they would have still been able to send a distress signal in transponder code.

Others have pointed to the history of the Boeing 777-200ER and how it had suffered a clipped wing tip in 2012 that was repaired by Boeing.

"Anytime there's been previous damage to an airplane, even though it's been repaired, and repaired within standards ... it kind of sends a warning flag," former 777 pilot Keith Wolzinger, now a civil aviation consultant with The Spectrum Group, told CNN. But experts agree that the 777 is a safe aircraft. "The reliability of airliner engines in general is impeccable these days," Wolzinger adds. "This is a safe plane."

4. Pilot Involvement

While there are no indications the pilots were involved in the plane’s disappearance, theorists are searching their history for clues.

Pilot Zahari Ahmad Shah, 53, was a veteran pilot who has flown with the airline for more than 25 years and has logged more than 18,000 flying hours. His colleagues describe him as a talented aviator.

"He's a jovial guy. Everyone who knew him liked him," a 43-year-old captain who knew Capt. Zaharie for nearly 25 years told the Wall Street Journal. "I flew as his co-pilot many times. He has always been a good pilot—very professional."

His co-pilot on Flight 370, Fariq Abdul Hamid, has been described differently. An Austrian television report said he allowed two women into the cockpit during a one-hour flight in December 2011 from Phuket, Thailand, to Kuala Lumpur.

"Throughout the entire flight they were talking to us, and they were actually smoking throughout the flight," Jonti Roos, one of the women involved, told 9News. "When I realized it was the exact same co-pilot and not only that but I had met him and I have photos in the cockpit with him, that was quite shocking."

5. Alien Abduction

No set of conspiracy theories are complete without the possibility of extra-terrestrial involvement. Twitter users took little time to connect the plane’s disappearance with a possible alien abduction of the aircraft. Others have cited a secret “U.S. carrier strike” and an extravagant promotional stunt for the remake of the TV series, Lost.

“Alien abduction, Time Slip? Possible but unlikely,” a person commenting on an article for The Economist writes. “The area is well known for it's Alien Activity (and Drugs!!) Not necessarily impossible, hence the authorites (sic) are seriuosly looking into this theory. You have to consider all things, no matter how bizarre they may seem.”

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