Crowdsourcing is increasingly becoming a means by which individuals and organizations seek to solve problems. This is due to the advantages of crowdsourcing such as greater access to experts, lower costs of access to such experts and ubiquitous opportunities. Platforms are, however, plagued with the challenge of collusion between workers. This intern implies that crowdsourcing service providers will be paying out money for no work done leading to losses. This paper presents a survey on crowdsourcing, types of malicious attacks, motivation for workers to collude, factors that lead to collusion and the way tasks are allocated on these platforms.