The United Nations said Monday more surveillance of Internet users is desirable to help in the investigation and prosecution of terrorists. A lack of \"internationally agreed framework for retention of data\" is a problem as are open WiFi networks in airports, cafes and libraries, a report released by the U.N. Office on Drugs and Crime said. Terrorists are increasingly turning to social networks and other sharing sites including Facebook, Twitter, YouTube and Dropbox, to spread \"propaganda,\" the report said. \"Potential terrorists use advanced communications technology often involving the Internet to reach a worldwide audience with relative anonymity and at a low cost,\" Yury Fedotov, executive director of the U.N. agency, said. \"One of the major problems confronting all law enforcement agencies is the lack of an internationally agreed framework for retention of data held by ISPs [Internet service providers],\" the report said. Europe has enacted a mandatory data-retention law, but the United States and most other countries have not followed suit, CNET reported. Privacy groups have been critical of such enacted or proposed legislation. The report said it would be desirable for certain websites, such as instant-messaging services and VoIP providers like Skype, keep records of \"communication over the Internet such as chat room postings.\"