JOHANNESBURG, South Africa - Mobs rampaged through poor suburbs of Johannesburg in a frenzy of anti-foreigner violence over the weekend, killing at least seven people, injuring dozens and forcing hundreds to seek refuge at police stations. The attacks capped a week of mounting violence that started in the sprawling township of Alexandra. Angry residents there accused foreigners — many of them Zimbabweans who fled their own country's economic collapse — of taking scarce jobs and housing. Police and government officials say organized criminals are also taking advantage of the anti-foreigner sentiment by using it as a cover for looting and...