Okay, problem isn't in ur pendrive problem in ur computer, some kind of viruses attack only removable drives, and user didn't find viruses in computer and also antivirus, you should download microsoft security essential here,--- http://windows.microsoft.com/en-IN/windows/security-essentials-download , and update this software insert ur pendrive and start virus scanning as a whole computer including ur pendrive ur problem will surely solve
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Okay, problem isn't in ur pendrive problem in ur computer, some kind of viruses attack only removable drives, and user didn't find viruses in computer and also antivirus, you should download microsoft security essential here,--- http://windows.microsoft.com/en-IN/windows/security-essentials-download ,
and update this software insert ur pendrive and start virus scanning as a whole computer including ur pendrive ur problem will surely solve