excel export warning when opening file

When my clients download an excel file via views data export they get the following error message when they try to open the file:
Error opening file: "The file format differs from the format that the file name extension specifies. Verify that the file is not corrupted and is from a trusted source before opening the file. Do you want to open the file now?"

Obviously, if they just choose yes the file opens just fine, but is there anything we can do to avoid flagging excel about the format differing from the file extension?

Thanks,