The firm said that when you send and receive attachments, they're auto scanned for viruses. If Gmail thinks your mail has viruses, it will attempt to clean the file or remove it.
But if it detects a virus and can't remove it, then you won't be able to download it.
And if you send an attachment which Gmail thinks is a virus, then you won't be able to fly it into the cyberaether until you kill the attachment.
Google doesn't say which tech it's using to implement the limited scan. ยต