<s>
An	O
air	B-Architecture
gap	I-Architecture
,	O
air	B-Architecture
wall	I-Architecture
,	O
air	B-Architecture
gapping	I-Architecture
or	O
disconnected	B-Architecture
network	I-Architecture
is	O
a	O
network	O
security	O
measure	O
employed	O
on	O
one	O
or	O
more	O
computers	O
to	O
ensure	O
that	O
a	O
secure	O
computer	B-Architecture
network	I-Architecture
is	O
physically	O
isolated	O
from	O
unsecured	O
networks	O
,	O
such	O
as	O
the	O
public	O
Internet	O
or	O
an	O
unsecured	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
.	O
</s>
<s>
It	O
means	O
a	O
computer	O
or	O
network	O
has	O
no	O
network	B-Protocol
interface	I-Protocol
controllers	I-Protocol
connected	O
to	O
other	O
networks	O
,	O
with	O
a	O
physical	O
or	O
conceptual	O
air	B-Architecture
gap	I-Architecture
,	O
analogous	O
to	O
the	O
air	B-Architecture
gap	I-Architecture
used	O
in	O
plumbing	O
to	O
maintain	O
water	O
quality	O
.	O
</s>
<s>
An	O
air-gapped	O
computer	O
or	O
network	O
is	O
one	O
that	O
has	O
no	O
network	B-Protocol
interfaces	I-Protocol
,	O
either	O
wired	O
or	O
wireless	O
,	O
connected	O
to	O
outside	O
networks	O
.	O
</s>
<s>
Many	O
computers	O
,	O
even	O
when	O
they	O
are	O
not	O
plugged	O
into	O
a	O
wired	O
network	O
,	O
have	O
a	O
wireless	B-General_Concept
network	I-General_Concept
interface	I-General_Concept
controller	I-General_Concept
(	O
WiFi	O
)	O
and	O
are	O
connected	O
to	O
nearby	O
wireless	O
networks	O
to	O
access	O
the	O
Internet	O
and	O
update	O
software	O
.	O
</s>
<s>
That	O
's	O
why	O
some	O
new	O
hardware	O
technologies	O
are	O
also	O
available	O
like	O
unidirectional	B-Device
data	I-Device
diodes	I-Device
or	O
bidirectional	O
diodes	O
(	O
also	O
called	O
electronic	O
airgaps	O
)	O
,	O
that	O
physically	O
separate	O
the	O
network	O
and	O
transportation	O
layers	O
and	O
copy	O
and	O
filter	O
the	O
application	O
data	O
.	O
</s>
<s>
One	O
way	O
to	O
transfer	O
data	O
between	O
the	O
outside	O
world	O
and	O
the	O
air-gapped	O
system	O
is	O
to	O
copy	O
data	O
on	O
a	O
removable	B-Device
storage	I-Device
medium	I-Device
such	O
as	O
a	O
removable	B-Device
disk	I-Device
or	O
USB	O
flash	O
drive	O
and	O
physically	O
carry	O
the	O
storage	O
to	O
the	O
other	O
system	O
.	O
</s>
<s>
That	O
's	O
why	O
another	O
way	O
to	O
transfer	O
data	O
,	O
used	O
in	O
appropriate	O
situations	O
like	O
critical	O
industries	O
,	O
is	O
to	O
use	O
data	B-Device
diodes	I-Device
and	O
electronic	O
airgaps	O
,	O
that	O
assure	O
a	O
physical	O
cut	O
of	O
the	O
network	O
by	O
a	O
specific	O
hardware	O
.	O
</s>
<s>
Sophisticated	O
computer	O
viruses	O
for	O
use	O
in	O
cyberwarfare	O
,	O
such	O
as	O
Stuxnet	O
and	O
agent.btz	O
have	O
been	O
designed	O
to	O
infect	O
air-gapped	O
systems	O
by	O
exploiting	O
security	O
holes	O
related	O
to	O
the	O
handling	O
of	O
removable	B-Device
media	I-Device
.	O
</s>
<s>
Life-critical	B-Application
systems	I-Application
,	O
such	O
as	O
:	O
</s>
<s>
Computers	O
used	O
in	O
aviation	O
,	O
such	O
as	O
FADECs	O
,	O
air	B-Application
traffic	I-Application
control	I-Application
systems	I-Application
,	O
and	O
avionics	O
;	O
</s>
<s>
The	O
engine	B-Device
control	I-Device
unit	I-Device
and	O
other	O
devices	O
on	O
the	O
CAN	B-Protocol
bus	I-Protocol
in	O
an	O
automobile	O
;	O
</s>
<s>
Many	O
of	O
these	O
systems	O
have	O
since	O
added	O
features	O
that	O
connect	O
them	O
during	O
limited	O
periods	O
of	O
time	O
to	O
the	O
organisation	O
's	O
internet	O
(	O
for	O
the	O
need	O
of	O
surveillance	O
or	O
updates	O
)	O
or	O
the	O
public	O
internet	O
,	O
and	O
are	O
no	O
longer	O
effectively	O
and	O
permanently	O
air	O
gapped	O
,	O
including	O
thermostats	O
with	O
internet	O
connections	O
and	O
automobiles	O
with	O
Bluetooth	B-Protocol
,	O
Wi-Fi	O
and	O
cellular	O
phone	O
connectivity	O
.	O
</s>
<s>
Limitations	O
imposed	O
on	O
devices	O
used	O
in	O
these	O
environments	O
may	O
include	O
a	O
ban	O
on	O
wireless	O
connections	O
to	O
or	O
from	O
the	O
secure	O
network	O
,	O
or	O
similar	O
restrictions	O
on	O
EM	O
leakage	O
from	O
the	O
secure	O
network	O
through	O
the	O
use	O
of	O
TEMPEST	B-Application
or	O
a	O
Faraday	O
cage	O
.	O
</s>
<s>
Scientists	O
in	O
2013	O
demonstrated	O
the	O
viability	O
of	O
air	B-Architecture
gap	I-Architecture
malware	O
designed	O
to	O
defeat	O
air	B-Architecture
gap	I-Architecture
isolation	O
using	O
acoustic	O
signaling	O
.	O
</s>
<s>
The	O
presence	O
of	O
IoT	B-Operating_System
devices	O
requiring	O
firmware	O
updates	O
can	O
also	O
complicate	O
matters	O
,	O
since	O
often	O
such	O
updates	O
cannot	O
be	O
centrally	O
managed	O
.	O
</s>
