So far, nothing.
“It is quite difficult to try to determine what could have happened,” said Cyrus Mody, a spokesman for the London-based International Maritime Bureau. “It would not go down without a trace, but in the shipping industry anything is possible.”
While the vessel’s fate remained a mystery, marine shipping experts tended to discount the idea that piracy was involved, noting that the ship was relatively small and carrying a low-value cargo of wood. They said it could have been hijacked by an organized criminal gang, perhaps in pursuit of drugs or some other illicit materials stashed on board, or to test the security environment in preparation for future attacks.
What is clear is that the Arctic Sea had a rough voyage from the outset. Flying a Maltese flag, it was traversing Swedish waters on July 24 when it was overtaken by a small boat and boarded by 8 to 12 men carrying firearms, the Malta Maritime Authority said in a statement. The intruders were “allegedly masked and wearing uniforms” with “police” written on them, the statement said, and harshly interrogated the crew, saying they were checking the ship for illegal drugs.
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“The members of the crew were allegedly assaulted, tied, gagged and blindfolded and some of them were seriously injured,” the statement said.
It is not clear who the men were. Officials from Sweden, which had jurisdiction over the waters where the search took place, said Swedish authorities were not involved, the Malta Maritime Authority said.
The ship’s captain radioed authorities after the 12-hour ordeal, saying the intruders had left in their small boat, Mr. Matveyev said. The captain said that he would keep the ship on course to Algeria.
A spokeswoman for the Maritime and Coastguard Agency in Britain said in an interview that the ship contacted the agency at 1:52 p.m. on July 28, when it was traveling through the Dover Strait between England and France.
“The Dover Coastguard didn’t notice anything unusual,” the spokeswoman said. “A lot of vessels go through the strait every day, and this one made a routine report and it didn’t seem anything was wrong.”
Mr. Matveyev said his company tracked the ship until July 31, when the ship radioed that it was off the coast of Portugal. The Malta Maritime Authority said the ship had not yet approached the Strait of Gibraltar, separating Spain from Morocco, “which indicates that the ship headed out in the Atlantic Ocean.”
A cargo ship spotted off the African island nation of Cape Verde could be the missing MV ''Arctic Sea''.

The Maltese flagged MV ''Arctic Sea'' disappeared off the  French coast sometime after July 29. Owned by the Russian Arctic Sea company she was operated by the Finnish Solchart Management company and had a Russian crew. 

French intelligence sources have found a ship matching the Arctic Sea's description about 400 Nautical miles north of São Vicente.
 
The ''Arctic Sea'' was on a scheduled route from the Finnish seaport of Pietarsaari to the Algerian seaport of  Béjaïa with a cargo of timber when it was boarded in Swedish waters between the islands Öland and Gotland on the  night of July 24. The alleged boarders left the ship the same day according to its crew and the ship continued her voyage although it would have been expected to anchor at the nearest port. 

The last official contact with the ship was with the Maritime and Coastguard Agency in Britain on July 28.  Viktor Matveyev, the director of Solchart Management says the ship radioed that it was off the coast of Portugal on July 31.  The 98-meter-long ship has so far not reached the Straits of Gibraltar and is now being sought by the Portuguese Navy and Russian Navy.

If proven this could be the first case of piracy in Europe in the modern era. There is speculation as to the reason for the ship's hijacking, as its cargo of wood, valued at 1.3 million euros, is not especially valuable. Suggestions include possible contraband, and the possibility of a commercial dispute between the crew or some other party and the ship's owners.