Nearly 57% of respondents reported they have been spammed via social networking sites.
Users being sent malware via social networks have risen by 69.8% in the past year to 36%.
Facebook is the social network that respondents believes poses the biggest security threat, the report published by IT security firm Sophos shows.
While Facebook is the largest social networking site in the world with 350 million users, 60% of internet users surveyed believe the site posted the biggest security risk.
Nearly 20% believed the biggest threat was posed by MySpace, followed by 17% who thought it was Twitter. Only 4% thought LinkedIn posed the biggest threat,
Graham Cluley, senior technology consultant for Sophos, said: "There is no doubt that simple changes could make Facebook users safer."