If you want to use DriveHQ as your main file storage, then you can use a web browser directly. You can also use DriveHQ FileManager or any FTP client software to drag and drop files and folders.
So far, we have not seen any virus that infects your files on DriveHQ from your PC. However, if your computer is infected with a virus, then somebody might be able to gain full access to your computer. In this case, if you save your DriveHQ username and password on your computer, your DriveHQ account could also be compromised. Of course, such chance is very rare.
If you use DriveHQ FileManager, you can create a sync task to automatically sync a remote folder with a local folder. You can set it to "Overwrite local files only" from Tools --> Manage Synchronization.