For simplicity, these instructions will refer to copying/moving a single file, but they apply equally well to groups of files and directories, which are copied recursively.
1. Open a file manager in the qube containing the file you wish to copy (the source qube), right-click on the file you wish to copy or move, and select `Copy to Other app qube...` or `Move to Other app qube...`.
4. If you wish, you may now move the file in the target qube to a different directory and delete the `/home/user/QubesIncoming/` directory when no longer needed.
The inter-qube file copy system is secure because it doesn't allow other qubes to steal the files that are being copied, and it doesn't allow the source qube to overwrite arbitrary files on the destination qube.
Moreover, this system doesn't use any sort of virtual block device for file copy.
Instead, we use Xen shared memory, which eliminates a lot of processing of untrusted data.
In this respect, the inter-qube file copy system provides even more security than file copy between two physically separated (air-gapped) machines!
(See [Software compartmentalization vs. physical separation](https://invisiblethingslab.com/resources/2014/Software_compartmentalization_vs_physical_separation.pdf) for more on this.)
However, one should keep in mind that performing a data transfer from *less trusted* to *more trusted* qubes is always potentially insecure if the data will be parsed in the target qube.
This is because the data that we copy could try to exploit some hypothetical bug in software running in the target qube.
For example, a seemingly-innocent JPEG that we copy from an untrusted qube might contain a specially-crafted exploit for a bug in a JPEG-parsing application in the target qube.
This is a general problem and applies to any data transfer from *less trusted* to *more trusted* qubes.
See also [this article](https://blog.invisiblethings.org/2011/03/13/partitioning-my-digital-life-into.html) for more information on this topic, and some ideas of how we might solve this problem in some future version of Qubes.