<s>
A	O
web	B-Protocol
beacon	I-Protocol
is	O
a	O
technique	O
used	O
on	O
web	O
pages	O
and	O
email	O
to	O
unobtrusively	O
(	O
usually	O
invisibly	O
)	O
allow	O
checking	O
that	O
a	O
user	O
has	O
accessed	O
some	O
content	O
.	O
</s>
<s>
Web	B-Protocol
beacons	I-Protocol
are	O
typically	O
used	O
by	O
third	O
parties	O
to	O
monitor	O
the	O
activity	O
of	O
users	O
at	O
a	O
website	O
for	O
the	O
purpose	O
of	O
web	O
analytics	O
or	O
page	O
tagging	O
.	O
</s>
<s>
They	O
can	O
also	O
be	O
used	O
for	O
email	B-Operating_System
tracking	I-Operating_System
.	O
</s>
<s>
When	O
implemented	O
using	O
JavaScript	O
,	O
they	O
may	O
be	O
called	O
JavaScript	B-Protocol
tags	I-Protocol
.	O
</s>
<s>
Using	O
such	O
beacons	B-Protocol
,	O
companies	O
and	O
organizations	O
can	O
track	O
the	O
online	O
behaviour	O
of	O
web	O
users	O
.	O
</s>
<s>
At	O
first	O
,	O
the	O
companies	O
doing	O
such	O
tracking	O
were	O
mainly	O
advertisers	O
or	O
web	O
analytics	O
companies	O
;	O
later	O
social	O
media	O
sites	O
also	O
started	O
to	O
use	O
such	O
tracking	O
techniques	O
,	O
for	O
instance	O
through	O
the	O
use	O
of	O
buttons	O
that	O
act	O
as	O
tracking	O
beacons	B-Protocol
.	O
</s>
<s>
In	O
2017	O
,	O
W3C	O
published	O
a	O
candidate	O
specification	O
for	O
an	O
interface	O
that	O
web	O
developers	O
can	O
use	O
to	O
create	O
web	B-Protocol
beacons	I-Protocol
.	O
</s>
<s>
A	O
web	B-Protocol
beacon	I-Protocol
is	O
any	O
of	O
several	O
techniques	O
used	O
to	O
track	B-Application
who	I-Application
is	I-Application
visiting	I-Application
a	I-Application
web	I-Application
page	I-Application
.	O
</s>
<s>
The	O
first	O
web	B-Protocol
beacons	I-Protocol
were	O
small	O
digital	O
image	O
files	O
that	O
were	O
embedded	O
in	O
a	O
web	O
page	O
or	O
email	O
.	O
</s>
<s>
The	O
image	O
could	O
be	O
as	O
small	O
as	O
a	O
single	O
pixel	O
(	O
a	O
"	O
tracking	B-Protocol
pixel	I-Protocol
"	O
)	O
and	O
could	O
have	O
the	O
same	O
colour	O
as	O
the	O
background	O
,	O
or	O
be	O
completely	O
transparent	O
.	O
</s>
<s>
When	O
a	O
user	O
opens	O
the	O
page	O
or	O
email	O
where	O
such	O
an	O
image	O
is	O
embedded	O
,	O
they	O
might	O
not	O
see	O
the	O
image	O
,	O
but	O
their	O
web	B-Application
browser	I-Application
or	O
email	B-Protocol
reader	I-Protocol
automatically	O
downloads	O
the	O
image	O
,	O
requiring	O
the	O
user	O
's	O
computer	O
to	O
send	O
a	O
request	O
to	O
the	O
host	O
company	O
's	O
server	B-Application
,	O
where	O
the	O
source	O
image	O
is	O
stored	O
.	O
</s>
<s>
This	O
basic	O
technique	O
has	O
been	O
developed	O
further	O
so	O
that	O
many	O
types	O
of	O
elements	O
can	O
be	O
used	O
as	O
beacons	B-Protocol
.	O
</s>
<s>
Currently	O
,	O
these	O
can	O
include	O
visible	O
elements	O
such	O
as	O
graphics	O
,	O
banners	O
,	O
or	O
buttons	O
,	O
but	O
also	O
non-pictorial	O
HTML	B-General_Concept
elements	I-General_Concept
such	O
as	O
the	O
frame	B-General_Concept
,	O
style	O
,	O
script	O
,	O
input	O
link	O
,	O
embed	O
,	O
object	O
,	O
etc.	O
,	O
of	O
an	O
email	O
or	O
web	O
page	O
.	O
</s>
<s>
The	O
identifying	O
information	O
provided	O
by	O
the	O
user	O
's	O
computer	O
typically	O
includes	O
its	O
IP	B-Protocol
address	I-Protocol
,	O
the	O
time	O
the	O
request	O
was	O
made	O
,	O
the	O
type	O
of	O
web	B-Application
browser	I-Application
or	O
email	B-Protocol
reader	I-Protocol
that	O
made	O
the	O
request	O
,	O
and	O
the	O
existence	O
of	O
cookies	B-Application
previously	O
sent	O
by	O
the	O
host	O
server	B-Application
.	O
</s>
<s>
The	O
host	O
server	B-Application
can	O
store	O
all	O
of	O
this	O
information	O
,	O
and	O
associate	O
it	O
with	O
a	O
session	B-Protocol
identifier	I-Protocol
or	O
tracking	O
token	O
that	O
uniquely	O
marks	O
the	O
interaction	O
.	O
</s>
<s>
This	O
company	O
could	O
store	O
all	O
of	O
its	O
images	O
on	O
one	O
particular	O
server	B-Application
,	O
but	O
store	O
the	O
other	O
contents	O
of	O
its	O
web	O
pages	O
on	O
a	O
variety	O
of	O
other	O
servers	O
.	O
</s>
<s>
For	O
instance	O
,	O
each	O
server	B-Application
could	O
be	O
specific	O
to	O
a	O
given	O
website	O
,	O
and	O
could	O
even	O
be	O
located	O
in	O
a	O
different	O
city	O
.	O
</s>
<s>
But	O
the	O
company	O
could	O
use	O
web	B-Protocol
beacons	I-Protocol
requesting	O
data	O
from	O
its	O
one	O
image	O
server	B-Application
to	O
count	O
and	O
recognize	O
individual	O
users	O
who	O
visit	O
different	O
websites	O
.	O
</s>
<s>
Rather	O
than	O
gathering	O
statistics	O
and	O
managing	O
cookies	B-Application
for	O
each	O
server	B-Application
independently	O
,	O
the	O
company	O
can	O
analyze	O
all	O
this	O
data	O
together	O
,	O
and	O
track	O
the	O
behavior	O
of	O
individual	O
users	O
across	O
all	O
the	O
different	O
websites	O
,	O
assembling	O
a	O
profile	O
of	O
each	O
user	O
as	O
they	O
navigate	O
through	O
these	O
different	O
environments	O
.	O
</s>
<s>
Web	B-Protocol
beacons	I-Protocol
embedded	O
in	O
emails	O
have	O
greater	O
privacy	O
implications	O
than	O
beacons	B-Protocol
embedded	O
in	O
web	O
pages	O
.	O
</s>
<s>
Through	O
the	O
use	O
of	O
an	O
embedded	O
beacon	B-Protocol
,	O
the	O
sender	O
of	O
an	O
email	O
–	O
or	O
even	O
a	O
third	O
party	O
–	O
can	O
record	O
the	O
same	O
sort	O
of	O
information	O
as	O
an	O
advertiser	O
on	O
a	O
website	O
,	O
namely	O
the	O
time	O
that	O
the	O
email	O
was	O
read	O
,	O
the	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
computer	O
that	O
was	O
used	O
to	O
read	O
the	O
email	O
(	O
or	O
the	O
IP	B-Protocol
address	I-Protocol
of	O
the	O
proxy	B-Application
server	I-Application
that	O
the	O
reader	O
went	O
through	O
)	O
,	O
the	O
type	O
of	O
software	O
used	O
to	O
read	O
the	O
email	O
,	O
and	O
the	O
existence	O
of	O
any	O
cookies	B-Application
previously	O
sent	O
.	O
</s>
<s>
"	O
Return-receipt-to	O
"	O
(	O
RRT	O
)	O
email	O
headers	O
can	O
also	O
trigger	O
sending	O
of	O
information	O
and	O
these	O
may	O
be	O
seen	O
as	O
another	O
form	O
of	O
a	O
web	B-Protocol
beacon	I-Protocol
.	O
</s>
<s>
Web	B-Protocol
beacons	I-Protocol
are	O
used	O
by	O
email	O
marketers	O
,	O
spammers	O
,	O
and	O
phishers	O
to	O
verify	O
that	O
an	O
email	O
is	O
read	O
.	O
</s>
<s>
To	O
some	O
extent	O
,	O
this	O
kind	O
of	O
email	B-Operating_System
tracking	I-Operating_System
can	O
be	O
prevented	O
by	O
configuring	O
the	O
email	B-Protocol
reader	I-Protocol
software	I-Protocol
to	O
avoid	O
accessing	O
remote	O
images	O
.	O
</s>
<s>
One	O
way	O
to	O
neutralize	O
such	O
email	B-Operating_System
tracking	I-Operating_System
is	O
to	O
disconnect	O
from	O
the	O
Internet	O
after	O
downloading	O
email	O
but	O
before	O
reading	O
the	O
downloaded	O
messages	O
.	O
</s>
<s>
(	O
Note	O
that	O
this	O
assumes	O
one	O
is	O
using	O
an	O
email	B-Protocol
reader	I-Protocol
that	O
resides	O
on	O
one	O
's	O
own	O
computer	O
and	O
downloads	O
the	O
emails	O
from	O
the	O
email	O
server	B-Application
to	O
one	O
's	O
own	O
computer	O
.	O
)	O
</s>
<s>
In	O
that	O
case	O
,	O
messages	O
containing	O
beacons	B-Protocol
will	O
not	O
be	O
able	O
to	O
trigger	O
requests	O
to	O
the	O
beacons	B-Protocol
 '	O
host	O
servers	O
,	O
and	O
the	O
tracking	O
will	O
be	O
prevented	O
.	O
</s>
<s>
But	O
one	O
would	O
then	O
have	O
to	O
delete	O
any	O
messages	O
suspected	O
of	O
containing	O
beacons	B-Protocol
or	O
risk	O
having	O
the	O
beacons	B-Protocol
activate	O
again	O
once	O
the	O
computer	O
is	O
reconnected	O
to	O
the	O
Internet	O
.	O
</s>
<s>
Web	B-Protocol
beacons	I-Protocol
can	O
also	O
be	O
filtered	B-Application
out	I-Application
at	I-Application
the	I-Application
server	I-Application
level	I-Application
so	O
that	O
they	O
never	O
reach	O
the	O
end-user	O
.	O
</s>
<s>
The	O
Beacon	B-Protocol
API	B-Application
(	O
application	B-Application
programming	I-Application
interface	I-Application
)	O
is	O
a	O
candidate	O
recommendation	O
of	O
the	O
World	O
Wide	O
Web	O
Consortium	O
,	O
the	O
standards	O
organization	O
for	O
the	O
web	O
.	O
</s>
<s>
It	O
is	O
a	O
standardized	O
API	B-Application
that	O
allows	O
to	O
send	O
data	O
back	O
to	O
server	B-Application
without	O
harming	O
user	O
experience	O
.	O
</s>
<s>
Use	O
of	O
the	O
Beacon	B-Protocol
API	B-Application
allows	O
tracking	O
without	O
interfering	O
with	O
or	O
delaying	O
navigation	O
away	O
from	O
the	O
site	O
,	O
and	O
is	O
invisible	O
to	O
the	O
end-user	O
.	O
</s>
<s>
Support	O
for	O
the	O
Beacon	B-Protocol
API	B-Application
was	O
introduced	O
into	O
Mozilla	B-Application
's	I-Application
Firefox	I-Application
browser	B-Application
in	O
February	O
2014	O
and	O
in	O
Google	B-Application
's	I-Application
Chrome	I-Application
browser	B-Application
in	O
November	O
2014	O
.	O
</s>
