Among employers that block social media websites, 77 percent say they do so to protect from security threats while 67 percent say it is to prevent decreased productivity, according to a new survey by MySammy, a software company that specializes in productivity measurement.

In fact, more than three in four respondents say social media hampers employee productivity; however, they don't know by how much. Sixty-five percent of respondents say they lack a means to measure employee productivity while on the computer, and 54 percent of respondents say social media helps employees perform their duties.

Although 76 percent of respondents say they're worried employee social media use could be bad for their reputation, only 38 percent of respondents report blocking social media websites in the workplace. Of respondents who allow social media access, 66 percent say they also don't record the time employees spend on them.