Securing installers in a external HD against viruses

Here’s the story, my job is to install oracle database on client’s computers and I’m using a USB external HD. Most of the time, those computers has a virus on it and tends to affect my HD and of course my installer. When I go back to the office, I need to scan my HD using Kaspersky (business ed.) and once it detected virus it will delete it together with some components of my installer (depending on the virus). So do you know any solution that can make files including executable file read only so it can not be infected by virus. Or any solution about this problem. Thank you!