Nearly one in five persons have snooped on the Facebook accounts of their friends, romantic partners or family members, using the victims’ own computers or cellphones, a new study.

Most people are concerned about the prospect of their social media accounts being hacked but University of British Columbia researchers reported that it’s actually people we know who frequently access our accounts without our permission.

“It’s clearly a widespread practice. Facebook private messages, pictures or videos are easy targets when the account owner is already logged on and has left their computer or mobile open for viewing,” said Wali Ahmed Usmani, lead study author.

People admitted to spying on their friends, family, and romantic partners out of simple curiosity or fun – for example, setting a victim’s status or profile picture to something humorous.

But other motives were darker, such as jealousy or animosity.

“Jealous snoops generally plan their action and focus on personal messages, accessing the account for 15 minutes or longer,” said computer science professor Ivan Beschastnikh, a senior author on the paper.

“And the consequences are significant: in many cases, snooping effectively ended the relationship.”

The findings, revealed after a survey of 1,308 US adult Facebook users, highlight the ineffectiveness of passwords and device PINs in stopping unauthorised access by insiders, added electrical and computer engineering professor Kosta Beznosov.

“There’s no single best defense – though a combination of changing passwords regularly, logging out of your account and other security practices can definitely help,” Beznosov suggested.

The paper is scheduled to be presented at the Association for Computing Machinery’s Conference on Human Factors in Computing Systems (CHI 2017) in May.