In the first of their two games in Scandinavia, Hammers came from behind twice to seal a comfortable victory thanks to double strikes from Joe Cole and Jermain Defoe, and one from Youssef Sofiane.
In front of an enthusiastic crowd of 2,117 - many of whom sported Hammers shirts - Glenn Roeder's men went a goal down after 18 minutes, but equalised just past the half hour mark when Cole weaved his way through the defence and tucked the ball past the Atvidabergs keeper.
The teams went in level at half-time, but the hosts restored their lead five minutes after the restart, when a cross from the left was headed past David James.
Once again, though, Hammers fought back to draw level, making it 2-2 in the 62nd minute. Anton Ferdinand raced down the right and his cross was helped on by Defoe to Sofiane - on as a half-time substitute for Fredi Kanoute - who slotted home from close range.
From that point on, the difference in class began to show, and Hammers grew stronger as the game wore on. Just two minutes after creating Sofiane's equaliser, Defoe got on the scoresheet himself when he planted Don Hutchison's cross into the net.
On 75 minutes, the England under-21 striker grabbed his second when Cole's pass found Sofiane, whose shot struck the post and rebounded kindly for Defoe to tap home.
The scoring was rounded off on 83 minutes, when a long punt forward from David James found Defoe, who capped off a fine individual performance by making it two assists to add to his two goals as he squared the ball for Cole to claim his own brace.
The scoreline made it nine goals in Hammers' two pre-season friendlies so far, following last week's 4-0 victory at Bournemouth, but Roeder's team will face a much sterner test in the second game of this four-day tour on Thursday, when they take on Swedish league champions Djurgardens IF, who are almost halfway through their current domestic campaign and are about to commence their Champions' League challenge.
Team: James (Bywater 83), Ferdinand, Repka, Dailly, Byrne, Hutchison (McMahon 68), Lee (D Noble 68), Cole (McClenahan 83), Garcia, Kanoute (Sofiane 45), Defoe.
Att: 2,117
Visit www.whufc.com on Thursday evening for full coverage and reaction from Hammers' friendly clash against Swedish champions Djurgardens IF.