The ship's disappearance confounded experts for weeks
Eight people have been arrested for hijacking the cargo ship Arctic Sea, Russia's defence minister says.
Anatoly Serdyukov said the group of suspects included Russian, Estonian and Latvian nationals.
The Arctic Sea went off the radar after passing through the English Channel in late July, but was found late on Sunday far south in the Atlantic.
Speculation swirled after the ship vanished, with suggestions of piracy, a mafia dispute or a commercial row.
The ship's owners had reported that the vessel was attacked 24 July in Swedish waters.
Russia's Interfax news agency quoted Mr Serdyukov as saying the hijackers had approached the Arctic Sea in a dinghy, claiming they needed help to repair their vessel.
But once on board the cargo ship, they threatened the crew with guns and forced them to sail south, the defence minister said.
The suspects include four Estonians, two Latvians and two Russians.
Mr Serdyukov said an investigation was under way aboard the Russian warship Ladny, where the Arctic Sea's 15-strong crew members and the suspected pirates were being questioned.
Carrying timber reportedly worth $1.8m (£1.1m), the 4,000-tonne Maltese-flagged vessel sailed from Finland and had been scheduled to dock in the Algerian port of Bejaia on 4 August.
The crew reported having been boarded by up to 10 armed men as the ship sailed through the Baltic Sea.
Before being found, the last known contact with the crew was when the Arctic Sea reported to British maritime authorities in Dover as it passed through the English Channel.
It was then sighted in the Bay of Biscay on 30 July.
Last weekend, police in Finland said a ransom demand had been made, but emphasised that they could not confirm its authenticity.
The Arctic Sea was eventually found on Sunday night 300 miles (480 km) off Cape Verde in the Atlantic Ocean.
Reports are emerging that eight people suspected of hijacking the 4,000-tonne Maltese registered vessel MV ''Arctic Sea'' have been arrested by the Russian Navy, and are being detained on the frigate ''Ladny''.
Artist's image of the MV ''Arctic Sea''.
Russian Defence Minister Anatoly Serdyukov confirmed that none of the detainees were members of the crew, and had boarded the vessel after approaching in a small dinghy, "using the threat of arms and demanded that the crew follow all of their orders without condition".

The vessel was found on Sunday off of the Cape Verde Islands, following over a week of searching. The vessel was previously last seen off the coast of France near Brest. There was much speculation as to the whereabouts of the vessel, after it did not arrive in Béjaïa, Algeria as scheduled on August 4, 2009.

The ship is said to be carrying a cargo of Finnish timber that is worth $1.8 million. 

According to the Estonian Security Police, among those detained were four Russians who were naturalized Estonian nationals, two Latvians and two Russians.