Nearly four in 10 (39 percent) web users aged 18 to 25 share passwords with friends and family, says AVG.
Research by the security firm, which has been conducted as part of a campaign to educate students about 'status jacking' and securing their social networking profiles, revealed that women are more likely to share their passwords, with 42 percent of females admitting to this, compared to just 28 percent of men.
While 78 percent secure their laptops with passwords, only 50 percent use passwords to protect their mobile phones. Men are more likely to secure their machines too, with 81 percent of males aged 18 to 25 password protecting their devices compared to 74 percent of women.
Furthermore, just over two in five (21 percent) secure handheld devices such as iPads.
AVG said web users aged 18 to 25 are aware of the need to use different passwords across different social networks, with 72 percent of British students admitting to doing this. However, nearly one in ten (nine percent) have downloaded a virus from a social network.
"The fact that most young adults secure their laptops and PCs is positive news, but the most worrying statistic is that four in ten share their passwords, something we do not advise doing," said AVG's Tony Anscombe.
"Sharing your passwords can leave your social networks open to status jacking and leaves your other online accounts, such as banking, vulnerable to attack."
AVG has also released a video featuring comedienne Holly Burns, which guides students and young adults through the dangers of status jacking.