What is a botnet?

According to Microsoft a bot is short for robot. Criminals distribute malicious software (also known as malware) that can turn your computer into a bot (also known as a zombie). When this occurs, your computer can perform automated tasks over the Internet, without you knowing it.

Criminals typically use bots to infect large numbers of computers. These computers form a network, or a botnet.

Criminals use botnets to send out spam e-mail messages, spread viruses, attack computers and servers. If your computer becomes a part of a botnet, your computer might slow down.

For ways to help protect your computer from becoming a zombie in a botnet, go to
http://www.microsoft.com/protect/computer/viruses/zombies.mspx

Turning off AutoPlay can Prevent USB Drives from Spreading Viruses

When you stick a thumb drive into a system, the AutoPlay feature launches the files and if infected it can also launch a worm and it can then spread the infection into your system. Turn off AutoPlay and prevent unnecessary headaches . Here's how:
On versions of Windows such as Windows XP Professional, Vista Ultimate
1. Click Start, click Run, enter gpedit.msc (launch Group Policy Editor);
2. XP users:Open Computer Configuration | Administrative Templates | System,
Vista users: Open Computer Configuration | Windows Components | AutoPlay Policies;
3. Find Turn Off AutoPlay in the right-hand pane and double-click it;
4. Choose Enabled and set it for All drives.utilities.
In any Windows version Try:
1. Launch the Registry editor (Start | Run | regedit);
2. Navigate to HKEY_CURRENT_USER\Software\Microsoft\Windows\
CurrentVersion\Policies\Explorer;
3. Double-click NoDriveTypeAutoRun in the right-hand pane and set its value to hexadecimal FF.
Now if you are too lazy to follow all this steps you can visit Panda Security at http://www.pandasecurity.com/usa/homeusers/downloads/usbvaccine/who offers a free "vaccine" program that will turn it off.