The biggest one is called Zeus, serves 3.6 million machines and can be used to send spam and denial of service.

The attacks from networks of computer s zombies , botnets, are already of concern in the U.S.. After installing malicious code on the user machine, these groups use the PC for sending mass e-mails unsolicited ( spam) .

The goal of these networks is to send millions of emails by compromised PCs and thus steal personal data and promote denial of service attacks, among other possibilities.

Learn the ten largest botnets in the United States. The survey was based on estimates from the security company Damballa, who analyzed the size and activity of the networks in the country.

1. Zeus
Compromised PCs: 3.6 million

Primary Use: the Trojan-horse uses a tracking technique of typing to steal sensitive data, such as user names, passwords, bank account numbers and credit cards. To this end, it includes codes of HTML pages for online banking login.

2. Koobface
Compromised PCs: 2.9 million

Primary Use: This malicious code spreads through social networks MySpace and Facebook messages with false or comments from supposed friends.

Clicking on a link to a video, the user is prompted to download an update - as a codec - which is actually a malware. The plague has already thousand variants , says security firm Kaspersky.

3. TidServ
Compromised PCs: 1.5 million

Primary Use: it spreads like a spam and attachment techniques using rootkits to hide in common services of Windows operating system, even in their mode of navigation safety. In general, he manages to hide most of its files and records in the system.

4. Trojan.Fakeavalert
Compromised PCs: 1.4 million

Primary Use: This botnet was used to send spam. His strategy, however, changed to download other malware, with a focus on security alerts and antivirus false.

5. TR / Dldr.Agent.JKH
Compromised PCs: 1.2 million

Primary Use: This Trojan-horse disclose encrypted data to remote areas of control and regularly receives instructions on them. Generally charged by other malicious code, the TR / Dldr.Agent.JKH is used as a clickbot for fraud by false clicks on ads, generating money with ads for the 'bot head.'

6. Monkif
Compromised PCs: 520 000

Main use: to download a program that displays unwanted advertisements on computers compromised.

7. Hamweq
Compromised PCs: 480 000

Primary Use: Also known as IRCBrute, or a worm that runs automatically, Hamweq copies itself in the system and to find any removable drive.

It has an efficient mechanism to spread, it creates records to enable automatic execution and includes the Explorer.exe file. The PC that controls the botnet can execute commands and receive information from all systems contaminated.

8. Swizzor
Compromised PCs: 370 000

Main use: download and run files through the Internet without the user's knowledge. From there, it installs an adware and other-a Trojan horse.

9. Guammima
Compromised PCs: 230 000

Primary Use: steal logins, passwords and other account information from online games by rootkit techniques. It spreads through removable media like USB hard drives.

10. Conficker
Compromised PCs: 210 000

Primary Use: This worm spread efficiently throughout the world, but not both in the United States. Also called Downadup, is complex and used to propagate malicious code. According to Kaspersky, Brazil is the third-most infected by Conficker .

Although it has been used to sell fake antivirus products, currently its only purpose would be spread by machinery. Experts, however, believe it may represent a greater danger greater.

Source: http://idgnow.uol.com.br/seguranca/2009/07/24/redes-de-pcs-zumbis-infestam-estados-unidos/