<s>
UDID	B-Operating_System
is	O
an	O
acronym	O
for	O
Unique	O
Device	O
Identifier	O
.	O
</s>
<s>
The	O
UDID	B-Operating_System
is	O
a	O
feature	O
of	O
Apple	O
's	O
devices	O
running	O
iOS	B-Application
,	O
tvOS	B-Operating_System
,	O
watchOS	B-Device
,	O
and	O
macOS	B-Application
.	O
</s>
<s>
It	O
is	O
a	O
unique	O
identifier	O
that	O
is	O
calculated	O
from	O
different	O
hardware	O
values	O
,	O
such	O
as	O
the	O
ECID	B-Operating_System
.	O
</s>
<s>
This	O
ID	O
is	O
also	O
used	O
to	O
detect	O
the	O
phone	O
or	O
to	O
communicate	O
with	O
it	O
while	O
restoring	O
the	O
IPSW	B-Operating_System
firmware	B-Application
.	O
</s>
<s>
Apple	O
mostly	O
uses	O
this	O
ID	O
to	O
identify	O
the	O
device	O
on	O
their	O
services	O
,	O
such	O
as	O
Apple	B-General_Concept
ID	I-General_Concept
and	O
iCloud	O
.	O
</s>
<s>
This	O
also	O
holds	O
the	O
Find	B-Operating_System
My	I-Operating_System
Activation	O
Lock	O
status	O
.	O
</s>
<s>
Starting	O
from	O
iOS	B-Operating_System
11	I-Operating_System
,	O
Apple	O
's	O
verification	O
server	O
will	O
check	O
the	O
device	O
's	O
UDID	B-Operating_System
before	O
it	O
could	O
be	O
set	O
up	O
.	O
</s>
<s>
If	O
the	O
device	O
's	O
UDID	B-Operating_System
is	O
malformed	O
or	O
not	O
present	O
in	O
Apple	O
's	O
database	O
,	O
the	O
device	O
cannot	O
be	O
activated	O
and	O
will	O
be	O
denied	O
access	O
to	O
the	O
verification	O
server	O
.	O
</s>
<s>
If	O
said	O
device	O
is	O
connected	O
to	O
iTunes	O
,	O
an	O
error	O
message	O
will	O
appear	O
stating	O
that	O
the	O
iPhone	B-Operating_System
could	O
not	O
be	O
activated	O
because	O
"	O
the	O
activation	O
information	O
could	O
not	O
be	O
obtained	O
from	O
the	O
device.	O
"	O
</s>
<s>
The	O
UDID	B-Operating_System
is	O
calculated	O
as	O
follows	O
for	O
the	O
Verizon	B-Operating_System
iPhone	I-Operating_System
4	I-Operating_System
:	O
</s>
