Corporate executives are concerned the use of Facebook and Twitter by employees could lead to the exposure of critical corporate data, according to a recent study. According to the study, carried out by email security vendor Proofpoint, 34 percent of US companies surveyed have been affected by the exposure of sensitive or embarrassing information during the past year. The June survey of 220 email decision-makers at companies with more than 1000 employees also found that 17 percent of companies have investigated the possible exposure of information on popular social networks like Facebook or LinkedIn. And 10 percent reported they have disciplined employees for violating social networking policies in the past year, while 8 percent have fired a worker for such offences. Recently, the US Marine Corps officially banned the use of social networking sites like Facebook and Twitter on military networks. One reason cited in the administrative directive: Social networks provide an easy conduit for information leakage to adversaries. "Businesses are still evaluating both the threat and opportunities presented by social networking," says Dan Olds, an analyst at Gabriel Consulting Group. "It is a way to get their message out to real people, but it can also be an avenue where confidential or embarrassing information can leak out as well. And this can be as innocent as an employee posting on Facebook that he is worried about layoffs, or they are extra busy because of customer complaints about their product. If these things get disseminated enough, it can cause real problems." Olds also points out that companies have to walk a fine line between advising employees to be cautious of what they post online and overstepping their bounds. "Businesses can't be seen as encroaching on their employees' free speech rights," he adds. "They need to put out reasonable guidelines and point out how innocent postings can be misconstrued," he says.