<s>
Evercookie	B-Application
(	O
also	O
known	O
as	O
supercookie	O
)	O
is	O
a	O
JavaScript	B-Language
application	O
programming	O
interface	O
(	O
API	B-General_Concept
)	O
that	O
identifies	O
and	O
reproduces	O
intentionally	O
deleted	O
cookies	B-Application
on	O
the	O
clients	O
 '	O
browser	B-Application
storage	O
.	O
</s>
<s>
Websites	O
that	O
have	O
adopted	O
this	O
mechanism	O
can	O
identify	O
users	O
even	O
if	O
they	O
attempt	O
to	O
delete	O
the	O
previously	O
stored	O
cookies	B-Application
.	O
</s>
<s>
In	O
2013	O
,	O
Edward	O
Snowden	O
leaked	O
a	O
top-secret	O
NSA	O
document	O
that	O
showed	O
Evercookie	B-Application
can	O
track	O
Tor	B-Application
(	O
anonymity	O
networks	O
)	O
users	O
.	O
</s>
<s>
Many	O
popular	O
companies	O
use	O
functionality	O
similar	O
to	O
Evercookie	B-Application
to	O
collect	O
user	O
information	O
and	O
track	O
users	O
.	O
</s>
<s>
Further	O
research	O
on	O
fingerprinting	O
and	O
search	O
engines	O
also	O
draws	O
inspiration	O
from	O
Evercookie	B-Application
's	O
ability	O
to	O
track	O
a	O
user	O
persistently	O
.	O
</s>
<s>
There	O
are	O
three	O
commonly	O
used	O
data	O
storages	O
,	O
including	O
HTTP	B-Application
cookies	I-Application
,	O
flash	B-Operating_System
cookies	I-Operating_System
,	O
HTML5	B-Application
Storage	I-Application
,	O
and	O
others	O
.	O
</s>
<s>
When	O
the	O
user	O
visits	O
a	O
website	O
for	O
the	O
first	O
time	O
,	O
the	O
web	O
server	O
may	O
generate	O
a	O
unique	O
identifier	O
and	O
store	O
it	O
on	O
the	O
user	O
's	O
browser	B-Application
or	O
local	O
space	O
.	O
</s>
<s>
Due	O
to	O
privacy	O
concerns	O
,	O
all	O
major	O
browsers	B-Application
include	O
mechanisms	O
for	O
deleting	O
and/or	O
refusing	O
cookies	B-Application
from	O
websites	O
.	O
</s>
<s>
In	O
response	O
to	O
the	O
users	O
 '	O
increased	O
unwillingness	O
to	O
accept	O
cookies	B-Application
,	O
many	O
websites	O
employ	O
methods	O
to	O
circumvent	O
users	O
 '	O
deletion	O
of	O
cookies	B-Application
.	O
</s>
<s>
Started	O
from	O
2009	O
,	O
many	O
research	O
teams	O
found	O
popular	O
websites	O
used	O
flash	B-Operating_System
cookies	I-Operating_System
,	O
ETags	O
,	O
and	O
various	O
other	O
data	O
storage	O
to	O
rebuild	O
the	O
deleted	O
cookies	B-Application
by	O
users	O
,	O
including	O
hulu.com,	O
foxnews.com,	O
spotify.com,	O
etc	O
.	O
</s>
<s>
In	O
2010	O
,	O
Samy	O
Kamkar	O
,	O
a	O
Californian	O
programmer	O
,	O
built	O
an	O
Evercookie	B-Application
project	O
to	O
further	O
illustrate	O
the	O
tracking	O
mechanism	O
with	O
respawning	O
across	O
various	O
storage	O
mechanisms	O
on	O
browsers	B-Application
.	O
</s>
<s>
Evercookie	B-Application
allows	O
website	O
authors	O
to	O
be	O
able	O
to	O
identify	O
users	O
even	O
after	O
said	O
users	O
have	O
attempted	O
to	O
delete	O
cookies	B-Application
.	O
</s>
<s>
Samy	O
Kamkar	O
released	O
v0.4	O
beta	O
of	O
the	O
evercookie	B-Application
on	O
September	O
13	O
,	O
2010	O
,	O
as	O
an	O
open	O
source	O
project	O
.	O
</s>
<s>
Evercookie	B-Application
is	O
capable	O
of	O
respawning	O
deleted	O
HTTP	B-Application
cookies	I-Application
by	O
storing	O
the	O
cookies	B-Application
on	O
multiple	O
different	O
storage	O
systems	O
typically	O
exposed	O
by	O
web	B-Application
browsers	I-Application
.	O
</s>
<s>
When	O
a	O
browser	B-Application
visits	O
a	O
website	O
with	O
the	O
Evercookie	B-Application
API	B-General_Concept
on	O
its	O
server	O
,	O
the	O
web	O
server	O
can	O
generate	O
an	O
identifier	O
and	O
store	O
it	O
on	O
various	O
storage	O
mechanisms	O
available	O
on	O
that	O
browser	B-Application
.	O
</s>
<s>
If	O
the	O
user	O
removes	O
some	O
but	O
not	O
all	O
of	O
the	O
stored	O
identifiers	O
on	O
the	O
browser	B-Application
and	O
revisits	O
the	O
website	O
,	O
the	O
web	O
server	O
retrieves	O
the	O
identifier	O
from	O
storage	O
areas	O
that	O
the	O
user	O
failed	O
to	O
delete	O
.	O
</s>
<s>
By	O
abusing	O
the	O
various	O
available	O
storage	O
mechanisms	O
,	O
Evercookie	B-Application
creates	O
persistent	O
data	O
identifiers	O
,	O
because	O
users	O
are	O
not	O
likely	O
to	O
clear	O
all	O
storing	O
mechanisms	O
.	O
</s>
<s>
From	O
the	O
list	O
provided	O
by	O
Samy	O
Kamkar	O
,	O
17	O
storage	O
mechanisms	O
could	O
be	O
used	O
for	O
the	O
v0.4	O
beta	O
Evercookie	B-Application
when	O
they	O
are	O
available	O
on	O
browsers	B-Application
:	O
</s>
<s>
Samy	O
Kamkar	O
claims	O
that	O
he	O
did	O
not	O
intend	O
to	O
use	O
the	O
Evercookie	B-Application
project	O
to	O
violate	O
internet	O
user	O
privacy	O
or	O
to	O
sell	O
to	O
any	O
parties	O
for	O
commercial	O
use	O
.	O
</s>
<s>
However	O
,	O
it	O
has	O
served	O
as	O
an	O
inspiration	O
for	O
other	O
commercial	O
websites	O
that	O
later	O
implemented	O
similar	O
mechanisms	O
to	O
restore	O
user-deleted	O
cookies	B-Application
.	O
</s>
<s>
The	O
Evercookie	B-Application
project	O
is	O
open	O
source	O
,	O
meaning	O
everyone	O
can	O
access	O
and	O
examine	O
the	O
code	O
,	O
or	O
use	O
the	O
code	O
for	O
any	O
purpose	O
.	O
</s>
<s>
The	O
project	O
incorporates	O
HTML5	B-Application
as	O
one	O
of	O
the	O
storage	O
mechanisms	O
,	O
which	O
was	O
released	O
6	O
months	O
before	O
the	O
project	O
and	O
gained	O
public	O
attentions	O
due	O
to	O
its	O
added	O
persistency	O
.	O
</s>
<s>
So	O
far	O
,	O
Firefox	O
browser	B-Protocol
plug-in	I-Protocol
"	O
Anonymizer	O
Nevercookie™	O
"	O
can	O
block	O
Evercookie	B-Application
respawning	O
.	O
</s>
<s>
The	O
storage	O
mechanisms	O
incorporated	O
in	O
the	O
Evercookie	B-Application
project	O
are	O
constantly	O
being	O
updated	O
,	O
adding	O
Evercookie	B-Application
's	O
persistency	O
.	O
</s>
<s>
As	O
it	O
incorporates	O
many	O
existing	O
tracking	O
methods	O
,	O
Evercookie	B-Application
provides	O
an	O
advanced	O
data	B-Application
tracking	I-Application
tool	O
that	O
reduces	O
the	O
redundancy	O
of	O
data	O
collection	O
methods	O
by	O
many	O
commercial	O
websites	O
.	O
</s>
<s>
With	O
its	O
inspiration	O
,	O
an	O
increasing	O
number	O
of	O
commercial	O
websites	O
used	O
the	O
idea	O
of	O
Evercookie	B-Application
,	O
and	O
they	O
add	O
upon	O
it	O
by	O
incorporating	O
new	O
storage	O
vectors	O
.	O
</s>
<s>
In	O
2014	O
,	O
a	O
research	O
team	O
at	O
the	O
Princeton	O
University	O
conducted	O
a	O
large	O
scale	O
study	O
of	O
three	O
persistent	O
tracking	O
tools	O
:	O
Evercookie	B-Application
,	O
canvas	B-Protocol
fingerprinting	I-Protocol
,	O
and	O
cookie	B-Application
syncing	O
.	O
</s>
<s>
The	O
team	O
crawled	O
and	O
analyzed	O
the	O
top	O
100,000	O
Alexa	O
websites	O
,	O
and	O
it	O
detects	O
a	O
new	O
storage	O
vector	O
,	O
IndexedDB	O
,	O
that	O
is	O
incorporated	O
into	O
Evercookie	B-Application
mechanism	O
and	O
used	O
by	O
weibo.com	O
.	O
</s>
<s>
Moreover	O
,	O
the	O
team	O
discovers	O
cookie	B-Application
syncing	O
is	O
used	O
in	O
conjunction	O
with	O
Evercookie	B-Application
.	O
</s>
<s>
Cookie	B-Application
syncing	O
allows	O
data	O
sharing	O
between	O
different	O
storage	O
mechanisms	O
,	O
facilitating	O
Evercookie	B-Application
's	O
respawning	O
process	O
in	O
different	O
storage	O
locations	O
on	O
users	O
 '	O
browsers	B-Application
.	O
</s>
<s>
The	O
team	O
also	O
discovered	O
instances	O
of	O
Flash	B-Operating_System
cookies	I-Operating_System
respawning	O
HTTP	B-Application
cookies	I-Application
,	O
and	O
HTTP	B-Application
cookies	I-Application
respawning	O
the	O
flash	B-Operating_System
cookies	I-Operating_System
on	O
the	O
commercial	O
websites	O
.	O
</s>
<s>
Those	O
two	O
mechanisms	O
are	O
different	O
from	O
the	O
Evercookie	B-Application
project	O
in	O
terms	O
of	O
the	O
number	O
of	O
storage	O
mechanisms	O
employed	O
,	O
but	O
they	O
possess	O
the	O
same	O
ideology	O
.	O
</s>
<s>
Among	O
the	O
sites	O
that	O
the	O
research	O
team	O
crawled	O
,	O
10	O
out	O
of	O
200	O
websites	O
used	O
flash	B-Operating_System
cookies	I-Operating_System
to	O
rebuild	O
HTTP	B-Application
cookies	I-Application
.	O
</s>
<s>
The	O
research	O
team	O
built	O
a	O
metadata-based	O
model	O
to	O
extract	O
users’	O
information	O
with	O
evercookie	B-Application
,	O
and	O
they	O
integrated	O
this	O
user	O
interest	O
model	O
into	O
the	O
search	O
engine	O
to	O
enhance	O
personalization	O
of	O
the	O
search	O
result	O
.	O
</s>
<s>
The	O
team	O
was	O
aware	O
that	O
traditional	O
cookie	B-Application
can	O
be	O
easily	O
deleted	O
by	O
experiment	O
subjects	O
thus	O
lead	O
to	O
incomplete	O
experiment	O
data	O
.	O
</s>
<s>
The	O
research	O
team	O
then	O
utilized	O
evercookie	B-Application
's	O
persistency	O
.	O
</s>
<s>
The	O
team	O
found	O
KISSmetrics	O
,	O
a	O
third	O
party	O
website	O
that	O
provides	O
marketing	O
analytical	O
tools	O
,	O
used	O
HTTP	B-Application
cookies	I-Application
,	O
Flash	B-Operating_System
cookies	I-Operating_System
,	O
ETags	O
,	O
and	O
some	O
but	O
not	O
all	O
storage	O
mechanisms	O
employed	O
in	O
Samy	O
Kamkar	O
's	O
Evercookie	B-Application
project	O
to	O
respawn	O
the	O
user	O
's	O
deleted	O
information	O
.	O
</s>
<s>
Other	O
popular	O
websites	O
,	O
such	O
as	O
hulu.com	O
and	O
spotify.com,	O
employed	O
KISSmetrics	O
to	O
respawn	O
HTML5	B-Application
and	O
HTTP	O
first	B-Application
party	I-Application
cookies	I-Application
.	O
</s>
<s>
On	O
August	O
4	O
,	O
2011	O
,	O
KISSmetrics	O
 '	O
CEO	O
Hiten	O
Shah	O
denied	O
KISSmetrics	O
 '	O
implementation	O
of	O
Evercookie	B-Application
and	O
other	O
tracking	O
mechanisms	O
mentioned	O
in	O
the	O
report	O
,	O
and	O
he	O
claimed	O
the	O
company	O
only	O
used	O
legitimate	O
first	B-Application
party	I-Application
cookie	I-Application
trackers	O
.	O
</s>
<s>
On	O
October	O
19	O
,	O
2012	O
,	O
KISSmetrics	O
agreed	O
to	O
pay	O
over	O
$	O
500,000	O
to	O
settle	O
the	O
accusation	O
and	O
promised	O
to	O
refrain	O
from	O
using	O
Evercookie	B-Application
.	O
</s>
<s>
In	O
2013	O
,	O
an	O
internal	O
National	O
Security	O
Agency	O
(	O
NSA	O
)	O
'	O
s	O
presentation	O
was	O
revealed	O
by	O
Edward	O
Snowden	O
,	O
suggesting	O
Evercookie	B-Application
's	O
use	O
in	O
government	O
surveillance	O
to	O
track	O
Tor	B-Application
users	O
.	O
</s>
<s>
The	O
TOR	B-Application
Blog	O
responded	O
to	O
this	O
leaked	O
document	O
in	O
one	O
post	O
,	O
assuring	O
that	O
TOR	B-Application
Browser	B-Application
Bundles	O
and	O
Tails	O
operating	O
system	O
provide	O
strong	O
protections	O
against	O
evercookie	B-Application
.	O
</s>
<s>
Evercookie	B-Application
,	O
and	O
many	O
other	O
emerged	O
new	O
technologies	O
in	O
persistent	O
data	B-Application
tracking	I-Application
,	O
is	O
a	O
response	O
to	O
internet	O
users	O
 '	O
tendency	O
of	O
deleting	O
cookie	B-Application
storage	O
.	O
</s>
<s>
Data	B-Application
tracking	I-Application
persists	O
,	O
however	O
.	O
</s>
