+=item B<--format=raw|qcow2|..> | B<--format>
+
+The default for the I<-a> option is to auto-detect the format of the
+disk image. Using this forces the disk format for I<-a> options which
+follow on the command line. Using I<--format> with no argument
+switches back to auto-detection for subsequent I<-a> options.
+
+If you have untrusted raw-format guest disk images, you should use
+this option to specify the disk format. This avoids a possible
+security problem with malicious guests (CVE-2010-3851). See also
+L</add-drive-opts>.
+