USB drives, or thumb / pen drives have the convenience of being small, lightweight and generally made for quick and small file exchanges. However, along with this advantage comes the risk of spreading viruses, trojans, worms and other malware to your computer.
This is especially relevant in case of offices and schools, where information and important work/study documents are often exchanged through USB drives. Undetectable (or worse, un-fixable) viruses and worms may enter your PC from USB sticks that you use. Though your friends are to be blamed for it, you can take a few preventive steps to stay away from virus infection.
Apart from using a regularly-updated antivirus, you should disable the Autorun feature of USB drives. Most viruses spread through the Autorun feature, as it requires no interference from the user.
Prevent viruses by disabling autorun
Click Start> Run> gpedit.msc and hit enter
Go to Computer Configuration > Administrative Templates > System. Scroll down to turn off autoplay and double click it.
In the window that comes up, click enabled radio button. Then select All drives in Turn off Autoplay. Note that you will be protected against external drives only (and not audio/video disks).