<s>
Private	B-Protocol
browsing	I-Protocol
is	O
a	O
privacy	O
feature	O
in	O
some	O
web	B-Application
browsers	I-Application
.	O
</s>
<s>
When	O
operating	O
in	O
such	O
a	O
mode	O
,	O
the	O
browser	B-Application
creates	O
a	O
temporary	O
session	B-Protocol
that	O
is	O
isolated	O
from	O
the	O
browser	B-Application
's	O
main	O
session	B-Protocol
and	O
user	O
data	O
.	O
</s>
<s>
Browsing	B-Protocol
history	I-Protocol
is	O
not	O
saved	O
,	O
and	O
local	O
data	O
associated	O
with	O
the	O
session	B-Protocol
,	O
such	O
as	O
Cookies	B-Application
,	O
Web	B-Protocol
cache	I-Protocol
,	O
are	O
cleared	O
when	O
the	O
session	B-Protocol
is	O
closed	O
.	O
</s>
<s>
These	O
modes	O
are	O
designed	O
primarily	O
to	O
prevent	O
data	O
and	O
history	O
associated	O
with	O
a	O
particular	O
browsing	O
session	B-Protocol
from	O
persisting	O
on	O
the	O
device	O
,	O
or	O
being	O
discovered	O
by	O
another	O
user	O
of	O
the	O
same	O
device	O
.	O
</s>
<s>
Private	B-Protocol
browsing	I-Protocol
modes	O
do	O
not	O
necessarily	O
protect	O
users	O
from	O
being	O
tracked	B-Application
by	O
other	O
websites	O
or	O
their	O
Internet	O
service	O
provider	O
(	O
ISP	O
)	O
.	O
</s>
<s>
Furthermore	O
,	O
there	O
is	O
a	O
possibility	O
that	O
identifiable	O
traces	O
of	O
activity	O
could	O
be	O
leaked	O
from	O
private	B-Protocol
browsing	I-Protocol
sessions	O
by	O
means	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
security	O
flaws	O
in	O
the	O
browser	B-Application
,	O
or	O
via	O
malicious	O
browser	B-Protocol
extensions	I-Protocol
,	O
and	O
it	O
has	O
been	O
found	O
that	O
certain	O
HTML5	B-Application
APIs	B-General_Concept
can	O
be	O
used	O
to	O
detect	O
the	O
presence	O
of	O
private	B-Protocol
browsing	I-Protocol
modes	O
due	O
to	O
differences	O
in	O
behavior	O
.	O
</s>
<s>
This	O
is	O
usually	O
why	O
some	O
people	O
mistake	O
private	B-Protocol
browsing	I-Protocol
for	O
a	O
VPN	B-Application
.	O
</s>
<s>
Apple	B-Application
's	I-Application
Safari	I-Application
browser	B-Application
was	O
one	O
of	O
the	O
first	O
major	O
web	B-Application
browsers	I-Application
to	O
include	O
this	O
feature	O
.	O
</s>
<s>
The	O
feature	O
has	O
since	O
been	O
adopted	O
in	O
other	O
browsers	B-Application
,	O
and	O
led	O
to	O
popularization	O
of	O
the	O
term	O
in	O
2008	O
by	O
mainstream	O
news	O
outlets	O
and	O
computing	O
websites	O
when	O
discussing	O
beta	O
versions	O
of	O
Internet	B-Application
Explorer	I-Application
8	I-Application
.	O
</s>
<s>
Adobe	B-Operating_System
Flash	I-Operating_System
Player	I-Operating_System
10.1	O
began	O
honoring	O
browser	B-Application
settings	O
and	O
private	B-Protocol
browsing	I-Protocol
status	O
in	O
regards	O
to	O
the	O
storage	O
of	O
local	B-Operating_System
shared	I-Operating_System
objects	I-Operating_System
.	O
</s>
<s>
Noted	O
uses	O
of	O
private	B-Protocol
browsing	I-Protocol
modes	O
include	O
hiding	O
undesirable	O
content	O
from	O
the	O
browsing	B-Protocol
history	I-Protocol
(	O
such	O
as	O
visits	O
to	O
adult-oriented	O
websites	O
)	O
,	O
performing	O
web	O
searches	O
that	O
are	O
not	O
algorithmically	B-Application
influenced	I-Application
by	O
prior	B-Algorithm
browsing	I-Algorithm
habits	I-Algorithm
or	I-Algorithm
the	I-Algorithm
user	I-Algorithm
's	I-Algorithm
recorded	I-Algorithm
interests	I-Algorithm
,	O
providing	O
a	O
"	O
clean	O
"	O
temporary	O
session	B-Protocol
for	O
a	O
guest	O
user	O
(	O
such	O
as	O
when	O
using	O
a	O
public	O
computer	O
)	O
,	O
and	O
using	O
websites	O
with	O
multiple	O
accounts	O
simultaneously	O
.	O
</s>
<s>
Private	B-Protocol
browsing	I-Protocol
has	O
also	O
been	O
used	O
as	O
a	O
means	O
to	O
circumvent	O
metered	O
paywalls	O
on	O
some	O
websites	O
.	O
</s>
<s>
In	O
a	O
survey	O
by	O
search	O
engine	O
DuckDuckGo	B-Application
,	O
48%	O
of	O
participants	O
declined	O
to	O
respond	O
(	O
leading	O
researcher	O
Elie	O
Bursztein	O
to	O
note	O
that	O
"	O
surveys	O
are	O
clearly	O
not	O
the	O
best	O
approach	O
to	O
understand	O
why	O
people	O
are	O
using	O
the	O
private	B-Protocol
browsing	I-Protocol
mode	O
because	O
of	O
the	O
embarrassment	O
factor	O
"	O
)	O
,	O
and	O
18%	O
listed	O
shopping	O
as	O
their	O
primary	O
use	O
of	O
private	B-Protocol
browsing	I-Protocol
modes	O
.	O
</s>
<s>
A	O
study	O
by	O
the	B-Operating_System
Mozilla	I-Operating_System
Foundation	I-Operating_System
found	O
that	O
most	O
sessions	O
lasted	O
only	O
about	O
10	O
minutes	O
,	O
but	O
that	O
there	O
were	O
periods	O
where	O
activation	O
increased	O
,	O
usually	O
around	O
11a.m.	O
</s>
<s>
Private	B-Protocol
browsing	I-Protocol
is	O
known	O
by	O
different	O
names	O
in	O
different	O
browsers	B-Application
.	O
</s>
<s>
It	O
is	O
a	O
common	O
misconception	O
that	O
private	B-Protocol
browsing	I-Protocol
modes	O
can	O
protect	O
users	O
from	O
being	O
tracked	B-Application
by	O
other	O
websites	O
or	O
their	O
Internet	O
service	O
provider	O
(	O
ISP	O
)	O
.	O
</s>
<s>
Such	O
entities	O
can	O
still	O
use	O
information	O
such	O
as	O
IP	B-Protocol
addresses	I-Protocol
and	O
user	O
accounts	O
to	O
uniquely	O
identify	O
users	O
.	O
</s>
<s>
Some	O
browsers	B-Application
have	O
partly	O
addressed	O
this	O
shortcoming	O
by	O
offering	O
additional	O
privacy	O
features	O
that	O
can	O
be	O
automatically	O
enabled	O
when	O
using	O
private	B-Protocol
browsing	I-Protocol
mode	O
,	O
such	O
as	O
Firefox	B-Application
's	O
"	O
Tracking	O
Protection	O
"	O
feature	O
to	O
control	O
use	O
of	O
web	O
trackers	O
(	O
which	O
has	O
since	O
been	O
rolled	O
into	O
a	O
larger	O
"	O
content	O
blocking	O
"	O
function	O
extended	O
outside	O
of	O
private	B-Protocol
browsing	I-Protocol
mode	O
)	O
,	O
and	O
Opera	B-Application
offering	O
an	O
in-house	O
VPN	B-Application
service	O
embedded	O
within	O
the	O
browser	B-Application
.	O
</s>
<s>
Brazilian	O
researchers	O
published	O
the	O
results	O
of	O
a	O
project	O
where	O
they	O
applied	O
forensic	O
techniques	O
(	O
namely	O
the	O
Foremost	O
data	O
carving	O
tool	O
and	O
Strings	O
program	O
)	O
to	O
extract	O
information	O
about	O
the	O
users	O
browsing	O
activities	O
on	O
Internet	B-Application
Explorer	I-Application
and	O
Firefox	B-Application
browsers	I-Application
with	O
their	O
private	B-Protocol
mode	I-Protocol
enabled	O
.	O
</s>
<s>
This	O
research	O
was	O
later	O
extended	O
to	O
include	O
the	O
Chrome	B-Application
and	O
Safari	B-Application
browsers	I-Application
.	O
</s>
<s>
The	O
gathered	O
data	O
proved	O
that	O
the	O
browsers	B-Application
 '	O
private	B-Protocol
mode	I-Protocol
implementations	O
are	O
not	O
able	O
to	O
fully	O
hide	O
users	O
 '	O
browsing	O
activities	O
and	O
that	O
browsers	B-Application
in	O
private	B-Protocol
mode	I-Protocol
leave	O
traces	O
of	O
activities	O
in	O
caching	O
structures	O
and	O
files	O
related	O
to	O
the	O
paging	B-Architecture
process	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Another	O
independent	O
security	O
analysis	O
,	O
performed	O
by	O
a	O
group	O
of	O
researchers	O
at	O
Newcastle	O
University	O
,	O
reported	O
a	O
range	O
of	O
potential	O
security	O
vulnerabilities	O
in	O
the	O
implementation	O
of	O
the	O
private	B-Protocol
modes	I-Protocol
across	O
Chrome	B-Application
,	O
Firefox	B-Application
,	O
Internet	B-Application
Explorer	I-Application
,	O
and	O
Safari	B-Application
,	O
including	O
that	O
;	O
</s>
<s>
Browser	B-Protocol
extensions	I-Protocol
could	O
still	O
record	O
history	O
if	O
they	O
were	O
active	O
in	O
private	B-Protocol
mode	I-Protocol
.	O
</s>
<s>
Although	O
Chrome	B-Application
and	O
Firefox	B-Application
have	O
since	O
required	O
extensions	O
to	O
be	O
enabled	O
on	O
an	O
opt-in	O
basis	O
for	O
their	O
private	B-Protocol
browsing	I-Protocol
modes	O
,	O
an	O
installed	O
extension	O
in	O
the	O
normal	O
mode	O
could	O
learn	O
the	O
user	O
's	O
activities	O
in	O
the	O
private	B-Protocol
mode	I-Protocol
by	O
measuring	O
the	O
usage	O
of	O
shared	O
computing	O
resources	O
.	O
</s>
<s>
Data	O
erasure	O
by	O
the	O
browser	B-Application
alone	O
is	O
found	O
to	O
be	O
insufficient	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
records	O
of	O
visited	O
websites	O
during	O
the	O
private	O
session	B-Protocol
can	O
be	O
retained	O
in	O
memory	O
for	O
a	O
long	O
time	O
even	O
after	O
the	O
private	O
session	B-Protocol
is	O
closed	O
.	O
</s>
<s>
In	O
addition	O
,	O
the	O
visited	O
website	O
records	O
are	O
usually	O
kept	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
in	O
the	O
local	O
DNS	B-Protocol
cache	O
.	O
</s>
<s>
Furthermore	O
,	O
the	O
modified	O
timestamps	O
of	O
certain	O
profile	O
files	O
saved	O
on	O
the	O
disk	O
may	O
reveal	O
if	O
the	O
private	B-Protocol
mode	I-Protocol
was	O
previously	O
turned	O
on	O
and	O
when	O
it	O
was	O
turned	O
on	O
.	O
</s>
<s>
Software	B-Error_Name
bugs	I-Error_Name
present	O
in	O
some	O
browsers	B-Application
were	O
found	O
to	O
seriously	O
degrade	O
the	O
security	O
of	O
the	O
private	B-Protocol
mode	I-Protocol
.	O
</s>
<s>
For	O
example	O
,	O
in	O
some	O
earlier	O
versions	O
of	O
Safari	B-Application
,	O
the	O
browser	B-Application
retained	O
private	B-Protocol
browsing	I-Protocol
history	O
records	O
if	O
the	O
browser	B-Application
program	O
was	O
not	O
closed	O
normally	O
(	O
e.g.	O
,	O
as	O
a	O
result	O
of	O
a	O
crash	O
)	O
,	O
or	O
if	O
the	O
user	O
acted	O
to	O
add	O
a	O
bookmark	O
within	O
the	O
private	B-Protocol
mode	I-Protocol
.	O
</s>
<s>
Depending	O
on	O
whether	O
the	O
session	B-Protocol
is	O
in	O
the	O
private	O
or	O
the	O
normal	O
mode	O
,	O
web	B-Application
browsers	I-Application
typically	O
exhibit	O
different	O
user	B-Application
interfaces	I-Application
and	O
traffic	O
characteristics	O
.	O
</s>
<s>
This	O
allows	O
a	O
remote	O
website	O
to	O
tell	O
if	O
the	O
user	O
is	O
currently	O
in	O
the	O
private	B-Protocol
mode	I-Protocol
,	O
for	O
example	O
,	O
by	O
checking	O
the	O
color	O
of	O
the	O
hyperlinks	O
or	O
measuring	O
the	O
time	O
of	O
writing	O
cookies	B-Application
.	O
</s>
<s>
Bugs	B-Error_Name
and	O
security	O
vulnerabilities	O
in	O
extensions	O
themselves	O
may	O
also	O
leak	O
personally	O
identifiable	O
data	O
from	O
private	B-Protocol
mode	I-Protocol
.	O
</s>
<s>
Implementations	O
of	O
the	O
HTML5	B-Application
FileSystem	O
API	B-General_Concept
can	O
be	O
used	O
to	O
detect	O
users	O
in	O
private	B-Protocol
mode	I-Protocol
.	O
</s>
<s>
In	O
Google	B-Application
Chrome	I-Application
,	O
the	O
FileSystem	O
API	B-General_Concept
was	O
not	O
available	O
in	O
Incognito	O
mode	O
prior	O
to	O
version	O
76	O
.	O
</s>
<s>
To	O
prevent	O
circumvention	O
of	O
paywall	O
policies	O
and	O
evasion	O
of	O
web	B-Application
tracking	I-Application
scripts	O
used	O
to	O
monetize	O
traffic	O
,	O
a	O
number	O
of	O
websites	O
—	O
including	O
The	O
New	O
York	O
Times	O
—	O
have	O
used	O
such	O
behavior	O
to	O
block	O
access	O
to	O
users	O
in	O
private	B-Protocol
browsing	I-Protocol
mode	O
,	O
and	O
requiring	O
them	O
to	O
subscribe	O
or	O
log	O
in	O
.	O
</s>
<s>
Chrome	B-Application
76	O
allows	O
the	O
FileSystem	O
API	B-General_Concept
to	O
be	O
used	O
in	O
Incognito	O
mode	O
;	O
explaining	O
the	O
change	O
,	O
Google	O
argued	O
that	O
the	O
ability	O
to	O
detect	O
the	O
use	O
of	O
Incognito	O
mode	O
infringes	O
on	O
users	O
 '	O
privacy	O
.	O
</s>
<s>
However	O
,	O
it	O
was	O
later	O
discovered	O
that	O
the	O
disk	O
space	O
quotas	O
for	O
the	O
API	B-General_Concept
differed	O
between	O
normal	O
and	O
Incognito	O
modes	O
,	O
providing	O
another	O
means	O
by	O
which	O
to	O
detect	O
Incognito	O
users	O
.	O
</s>
<s>
Scripts	O
have	O
also	O
been	O
developed	O
to	O
detect	O
private	B-Protocol
browsing	I-Protocol
mode	O
on	O
other	O
browsers	B-Application
,	O
such	O
as	O
Firefox	B-Application
.	O
</s>
