More than one in ten social networkers thinks their account has been hacked, says Moneysupermarket.com.
Of those potential hackers, most said they accessed the account because they suspected their partner was having affair.
However, playing practical jokes on someone, checking what was being said behind their back and stalking were also among the most popular reasons for hacking into someone's account.
Two thirds of web users that have had their account hacked said they had changed their passwords to ensure it didn't happen again, while a quarter closed their account.
James Parker, manager of mobiles and broadband at moneysupermarket.com said, "People need to take hacking seriously and follow advice to safeguard themselves against attempts to access their account and personal information".
"Social networking sites have become a normal part of people's everyday lives but it is important to remember that hundreds of people could have access to your private details, especially if your email address is linked to both your public profile and then used for things like internet banking."