Dead Snow

A woman, Sara, is being chased through the snows of Norway. She is ultimately cornered and eaten by zombies in World War II Nazi SS uniforms.
Seven students on Easter vacation arrive at a small cabin near Ãksfjord. The cabin is owned by Sara, Vegard's girlfriend. The group begins to drink and party until a mysterious hiker arrives. He tells them the dark history of the region; during World War II, a force of Einsatzgruppe, led by StandartenfÃ¼hrer Herzog, occupied the area. For three years, the Nazis abused and tortured the local people. Near the end of the war, with Germany's defeat looming, the soldiers looted all the town's valuables. However, the citizens staged an uprising and ambushed them, killing many. The survivors, including Herzog and Michael Schwab, were chased into the mountains, and it was assumed that they all froze to death. The hiker then continues on his way. That night, Vegard wakes to a figure placing something beneath the floorboards of the cabin. He calls out, believing it to be Sara, but she ignores him and leaves. Vegard follows, and finds her outside covered in blood. Vegard suddenly jolts awake in his bed, revealing it was a dream. Meanwhile, the hiker has set up camp in the mountains and is eating dinner when he is disturbed by a noise outside. He investigates, and is attacked and killed by a zombie.
The next morning, Vegard, out looking for Sara, discovers the hiker's body. He searches the area, falls through the snow into a cave, and is knocked unconscious. After sunset, Erlend finds an old wooden box filled with valuables and golden trinkets. They celebrate, and one of them pockets a gold coin. They eventually return the rest of the treasure to the box. Erlend goes to the outhouse where he and Chris have sex. Afterwards, Erlend return to the cabin, and drops a gold coin. Chris is attacked by a zombie, and killed. The others leave the cabin to look for her, and find Sara's rucksack buried in the snow.
Upon returning to the cabin, they are attacked. Erlend is killed in an attempt to defend the cabin, and the others secure the building. Vegard comes around in the cave, discovering German firearms and helmets, as well as Sara's severed head. He is attacked, but escapes to the surface, where he is confronted by a zombie. Vegard stabs the zombie in the eye, but is knocked from the cliff side by a second assailant. Vegard is bitten in the neck by the zombie, whilst the two hang from the cliff using an intestine as rope. He climbs back to the snowmobile, stitches his wounds, and mounts a machine gun to his snowmobile.
Meanwhile, the remaining four students decide to split up. The two men, Martin and Roy, attempt to distract the zombies, while the two women, Hanna and Liv, run for the cars and go for help. En route to the cars, the girls are ambushed. Liv is knocked out by the zombies and awakens to them pulling out her intestines. Using a hand grenade, she commits suicide and kills her assailants. Hanna leads a zombie to a cliff edge, breaks the ice, and they fall. The pair survive, and Hanna kills the zombie.
Martin and Roy accidentally set fire to the cabin with Molotov cocktails. They escape, and arm themselves with power tools. More zombies attack, but they are aided by Vegard. During the attack Vegard is killed and Martin accidentally kills Hanna, who has returned to the cabin. Herzog arrives, leading a group of zombies. They attack, and Martin is bitten on the arm. To avoid becoming infected, he cuts off his arm with a chainsaw. After killing the remaining undead, Martin and Roy attack Herzog, who calls upon hundreds of zombies, that rise from under the snow. Whilst running from their attackers, Roy is hit in the head by a hammer, disemboweled by a tree branch, and killed by Herzog, who retrieves a watch from his pocket.
Martin realises the zombies' intent, and retrieves the box from the ruined cabin. He returns the box to Herzog, and escapes to the car. There, he finds a gold coin in his pocket, just as Herzog smashes the window of the car.

Question: How long did the Nazis abuse and torture the local people?
Answer: for three years