Hundreds of anti-government protesters - many wearing white masks - converged on Bangkok's shopping district on Sunday. The demonstration by the 'V for Thailand' movement  was the fourth this month outside the CentralWorld complex in the heart of the city. Little is known about the leaders or political allegiances of V for Thailand, but the group has swiftly developed a major social media profile railing against Prime Minister Yingluck Shinawatra and her brother Thaksin Shinawatra.