London attack raises some vital questions

The London attack on March 22 in which five people, including the attacker and a policeman, were killed and 40 injured is another potent warning against terrorism.

The United Kingdom has been tightening its security measures after the 2005 terrorist attack in London that claimed more than 50 lives. The measures include sharing information with other countries, strengthening the police force, as well as providing professional training to counter-terrorism forces. But, as the March 22 attack showed, it is still difficult even for a country with the tightest security to prevent a terrorist attack.

Last week's London attack also showed new trends in terrorism, such as "lone wolf" attacks. These "lone wolves" are sometimes helped by one or two residents to launch attacks on unsuspecting innocent people. The number of lone wolf attacks has been rising since 2000. In May 2013, two terrorists killed a soldier in London; in March this year, a man, later identified as an extremist, was shot dead while trying to snatch the weapon of a female solider at Orly Airport in France. All those were so-called lone-wolf attacks.