President Bill Clinton's new measures to protect America's computer systems from hackers and viruses comes amid increased global concerns over the threat of cyber-terrorism.

Law enforcement agencies say the electronic age has made crime more sinister and criminals harder to catch.

All computer networks that control critical systems, such as air traffic control or nuclear power plants, are potentially at risk from hackers and viruses.

But because electronic messages plotting crimes can be encrypted, hackers can easily evade detection.

Key to solving cybercrime

Computer experts say one possible way to combat cyber-terrorism is to give law agencies access to encryption keys that are used to scramble information.

This would give police and other law enforcement bodies powers to intercept e-mails, read confidential documents and tap into systems when cyber-crime is suspected.

But there's been debate about whether such a system would be workable in practice and whether it might infringe civil liberties.

Other measures include developing new tools to detect computer viruses and training a new generation of computer security specialists to deal with hackers