Friends many of your PC/laptop's normally gets virus because of Pen Drives or USB devices (Even PC's who are not connected to network ). Some Virus like Ravmon Virus , Heap41a worm which are not detected by anti virus normally spreads mostly by the Pen Drives . In such a case what can you do to prevent your PC from getting infected with Virus that spreads through USB devices or Pen Drives ?
You can protect your PC by just following the simple steps below . It won't take much time. 
Connect your Pen Drive or USB drive to your computer . 
Now a dialogue window will popup asking you to choose among the options as shown in the figure.     
Don't choose any of them , Just simply click Cancel.               
 *Now go to Start--> Run and type cmd to open the Command Prompt window ..                                   
 *Now go to My Computer and Check the Drive letter of your USB drive or Pen Drive . ( E.g. If it is written Kingston (I:) , then I: will be the drive letter ..)                                                   
 *In the Command Window ( cmd ) , type the drive letter: and Hit Enter ..                                                                                                                         
*Now type dir/w/o/a/p and Hit Enter   
*You will get a list of files . In the list , search if anyone of the following do exist     
1.         Autorun.inf                                                                                                                     
 2.         New Folder.exe                                                                                                                 
 3.         Bha.vbs                                                                                                                           
 4.         Iexplore.vbs                                                                                                                                   
 5.         Info.exe                                                                                                                                               
 6.         New_Folder.exe                                                                                                                           
 7.         Ravmon.exe                                                                                                                                     
 8.         RVHost.exe or any other files with .exe Extension .     
  
If you find any one of the files above , Run the command attrib -h -r -s -a *.* and Hit Enter. 
Now Delete each File using the following Command del filename ( E.g del autorun.inf ) . 
That's it . Now just scan your USB drive with the anti virus you have to ensure that you made your Pen Drive free of Virus.