According to a survey by security firm Sophos, half of all companies block employees from accessing Facebook at work, citing worries about the site’s impact on productivity and security.

Sophos notes that many Facebook profile pages contain users’ current employment details, which cybercriminals could use with other stolen information to commit corporate fraud or infiltrate company networks. Forty-one percent of Facebook users are prepared to divulge personal information to a complete stranger, Sophos’s research reveals.

“There’s a sense that our lives have to be an open book,” says Mitch Ratcliffe, a technology entrepreneur. “Sharing lots of information about yourself may appear appealing to people, but you’re also offering a lot of reasons not to associate with you.” Companies look for employees with discretion, he notes. “I’m not going to hire people who tell everything about themselves…it’s not particularly good for business relationships.”