At the moment, the ITU said the sheer number of identifiers and passwords required from computer users made it nearly inevitable that they repeat codes.
"This may cause security breaches, and leave them vulnerable to the machinations of identity thieves ever increasing in number and inventiveness," it said in its 2006 Internet report, released ahead of a major meeting of governments and industry officials in Hong Kong.
"The lack of coordination in identification systems is a source of growing inconvenience to users and needs to be addressed rapidly," it said.
The agency also highlighted risks to privacy from widespread Internet use, especially from marketers tracking the preferences and traffic of browsers across a variety of sites.
If people have confidence in the way such information is stored and used, the ITU said there might be no problem from the proliferation of "cookies" and other data-capturing tools, often used for targeted online advertising.
But it warned that a breakdown in consumer trust could impede the future expansion of Internet-based commerce.