Two years ago, a triumphant US President Barack Obama declared "justice has been done" after al-Qaida founder Osama bin Laden was killed by US special forces operating inside Pakistan. However, the ghost of terrorism and extremism continues to haunt many parts of the world, including the United States, raising concerns about the prospects for the world's anti-terror campaign.

Many in the world expected it would be the end of al-Qaida when bin Laden died. However, despite the fact that al-Qaida has been dealt a heavy blow, what has happened in the past two years indicates terrorist groups are taking advantage of the Internet and regional social unrest to reorganize.

The jihadist groups, which were squeezed out of Mali by Western intervention, have moved north, crossing the Sahara through Algeria and Niger to Libya, posing a threat to Libya's bleak security outlook.

And it is no longer a secret that many members of al-Qaida have penetrated into Syria, connived with the opposition forces and set up their own strongholds there, fueling growing concern in the Western world. There have been reports that al-Qaida has been recruiting new members in the Middle East and North Africa, through schools operating online, which not only spread extremist ideas, but also teach people how to make bombs and conduct terrorist activities.

US media have also highlighted that social networks, such as Twitter and Facebook, are poised to become a hotbed for terrorism, as they enable extremists to forge connections.

All these are worrying signals that terrorism remains rampant in some parts of the world, and the Boston bombing and last week's killings in Xinjiang, Northwest China, both laid bare the ferocity of terrorists, whether they work alone or in groups, and the severe damage they can inflict.

As no country can claim to be immune from the threat of terror, the world community should not be daunted, countries must work together against terrorist activities. They should stay vigilant against the new trends in international terrorism and step up efforts to remove the soil that allows terrorism and extremism to grow.

Without addressing the root causes of terror, such as poverty, injustice and social inequality, military counter attacks alone are not enough to rid the world of the scourge of terror.