"Almost two-thirds (63 per cent) of sys administrators fear that workers share too much personal information through social networking websites, according to a poll by IT security firm Sophos."

So why do they not block them?

"Although one third of organisations still reckon timewasting on social networking sites is the greater issue with sites such as Twitter and Facebook, malware and data leakage were also cited as concerns by many firms."

This shows that the sysadmins would have the backing from the management for a block