['This', 'paper', 'will', 'present', 'the', 'security', 'limitations', 'in', 'the', 'single', 'Cloud', 'and', 'the', 'usefulness', 'of', 'adopting', 'rather', 'Multi', '-', 'Clouds', 'strategy', 'to', 'reduce', 'security', 'risks', ',', 'through', 'the', 'use', 'of', 'DepSky', 'which', 'is', 'a', 'virtual', 'storage', 'system', 'that', 'ensures', 'better', 'availability', 'and', 'high', 'confidentiality', 'of', 'data', '.']