Viruses and spam are not as dangerous as means to distribute them. Cyber attacks wouldn’t be that successful without huge networks that make them possible. Homeland Security (USA) even declared botnets a threat to national security to accent the gravity of the problem.
The exact numbers of zombie computers are not know, however approximate measurements reveal hundreds of thousands of employed machines. These computers connected into gigantic botnets can be used for various cyber crimes. Botnets are problem for the whole world, not only the USA; however it’s the first case when they are decried an issue in State level. Networks of zombie computers were used to attack several websites of Church of Scientology and Estonian government. Other not so famous cases targeted credits card thefts and spam distribution.
Botnets are difficult to detect, but it’s even harder to find out who are responsible for the attacks. US Homeland Security Secretary Michael Chertoff hadn’t revealed what tactics are chosen to fight this problem, but he ensured that they take cyber crimes seriously.