US officials said that "real and growing" threats to US computer and telecommunications networks were behind the holding of <A HREF="http://news.yahoo.com/s/afp/20080313/tc_afp/uscomputerinternetsecurity">the largest-ever cyber-security exercises</A> this week.

Computer security experts from five countries, more than 40 private sector companies, and numerous government and state agencies are spending a week fielding simulated "real-world," on-line attacks on the computer systems of government bodies, corporations, transportation and other key industries.