In an accompanying blog post, the MoD states:
“Social networking sites are great for keeping in touch with family and friends, and letting the world know what you’re up to. The Online Engagement Guidelines make it clear that we encourage the safe and responsible use of social networking sites. Remember that there may be those who are using such sites for unsavoury reasons. These range from criminals looking for ways to con you or steal your identity, to those who may wish us harm. While it is unlikely that you’ll fall victim, you should be aware of the risk.”
(via UK government schools military on pitfalls of social media - TNW UK)
