Half of businesses are restricting employees' access to social networking site Facebook, due to concerns about productivity and security.
According to research by security company Sophos, 43 percent of workers polled said their employer blocks Facebook access completely.
A further seven percent said access is restricted depending on whether it is required for a particular job.
Graham Cluley, senior technology consultant at Sophos, told ZDNet Asia's sister site Silicon.com: "I think it's a growing concern for employers for a number of reasons. The most pressing concern at the moment is one of productivity."
Cluley said: "Some people are spending an inordinate amount of time on non-work related websites."
Cluley added it is difficult to tell when people are using a social networking site when they are sat at a computer.
The issue of security was also raised by the Sophos research. In a separate poll by the company, 66 percent of workers said they are concerned about colleagues sharing information on Facebook.
Details such as employment history and mobile numbers have been found on the site and could be used for identity theft or to launch corporate phishing attacks.
Sophos research found 41 percent of Facebook users are willing to divulge personal information to complete strangers.
Cluley said: "Everyone's just sort of letting it all hang out online without thinking who might be watching."
Facebook told Silicon.com it provides users with the ability to hide personal information and "welcomes every opportunity to educate users about how to protect their data online".
Of the 50 percent of companies that allow access to Facebook, Cluley said some view it as a valuable networking tool while others are nervous about the possibility of an employee backlash to a ban.
Tim Ferguson of Silicon.com reported from London
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