With the advancing computer technology, and the computer becoming an essential part of life, most of the data that a person, company or a government has would be on the computer. Does someone hack those computers, leaving a worm in the system that not only destroys all the data, but steals it, the damage could be irreversible. This is a relatively new method that criminals, companies and countries around the world are using as a source of attack on the others' systems. This kind of attack is sneakier and relatively unpredictable, hardly identifiable, and hence is hard to be reversed once it occurs.An example is the Iranian Nuclear reactor attacked using the Stuxnet virous, months elapsed before the Iranian authorities discovered the attack and responded. Some experts say that the cyber attacks on US systems in future can be predicted as equivalent to many hurricanes.
Another example is the Korean war going on right now, that was backed by cyber war on behalf of North Koreans against the Computer Savvy South Koreans. The sophisticated cyber attacks against the South Koreans changed into the conventional war more recently, while North Korea claims that it was started by South Korea. Although there are many other factors that cooked up this attack, but another form of war that backed up this one has been the cyber war that North Korea has been engaged in against South Korea.
British authorities are also accordingly shaping up their security systems, focusing now more on the cyber attacks rather than the military (although these are not phased out either). They say that AlQaeda being dealt through military might have weekened apparently, but in real terms, they have actually diversified and are focusing on 'Softer targets' (cyber war) now.
The security officials of USA claim that there are more than 100 countries involved in attacking America's systems.