<s>
The	O
user	O
credentials	O
are	O
typically	O
some	O
form	O
of	O
username	O
and	O
a	O
matching	O
password	O
,	O
and	O
these	O
credentials	O
themselves	O
are	O
sometimes	O
referred	O
to	O
as	O
a	O
login	B-General_Concept
.	O
</s>
<s>
In	O
practice	O
,	O
modern	O
secure	O
systems	O
often	O
require	O
a	O
second	O
factor	O
such	O
as	O
email	O
or	O
SMS	B-Device
confirmation	O
for	O
extra	O
security	O
.	O
</s>
<s>
Social	O
login	B-General_Concept
allows	O
a	O
user	O
to	O
use	O
existing	O
user	O
credentials	O
from	O
a	O
social	O
networking	O
service	O
to	O
sign	O
in	O
to	O
or	O
create	O
an	O
account	O
on	O
a	O
new	O
website	O
.	O
</s>
<s>
Once	O
the	O
user	O
is	O
logged	O
in	O
,	O
the	O
login	B-General_Concept
token	O
may	O
be	O
used	O
to	O
track	O
what	O
actions	O
the	O
user	O
has	O
taken	O
while	O
connected	O
to	O
the	O
site	O
.	O
</s>
<s>
Logging	O
out	O
may	O
be	O
performed	O
explicitly	O
by	O
the	O
user	O
taking	O
some	O
actions	O
,	O
such	O
as	O
entering	O
the	O
appropriate	O
command	B-Application
or	O
clicking	O
a	O
website	O
link	O
label	O
as	O
such	O
.	O
</s>
<s>
It	O
can	O
also	O
be	O
done	O
implicitly	O
,	O
such	O
as	O
by	O
the	O
user	O
powering	O
off	O
his	O
or	O
her	O
workstation	O
,	O
closing	O
a	O
web	B-Application
browser	I-Application
window	O
,	O
leaving	O
a	O
website	O
,	O
or	O
not	O
refreshing	O
a	O
website	O
within	O
a	O
defined	O
period	O
.	O
</s>
<s>
A	O
login	B-General_Concept
page	O
may	O
have	O
a	O
return	O
URL	O
parameter	O
,	O
which	O
specifies	O
where	O
to	O
redirect	O
back	O
after	O
logging	O
in	O
or	O
out	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
websites	O
that	O
use	O
cookies	B-Application
to	O
track	O
sessions	O
,	O
when	O
the	O
user	O
logs	O
out	O
,	O
session-only	O
cookies	B-Application
from	O
that	O
site	O
will	O
usually	O
be	O
deleted	O
from	O
the	O
user	O
's	O
computer	O
.	O
</s>
<s>
In	O
addition	O
,	O
the	O
server	O
invalidates	O
any	O
associations	O
with	O
the	O
session	O
,	O
thereby	O
making	O
any	O
session-handle	O
in	O
the	O
user	O
's	O
cookie	B-Application
store	O
useless	O
.	O
</s>
<s>
This	O
feature	O
comes	O
in	O
handy	O
if	O
the	O
user	O
is	O
using	O
a	O
public	O
computer	O
or	O
a	O
computer	O
that	O
is	O
using	O
a	O
public	B-Application
wireless	I-Application
connection	I-Application
.	O
</s>
<s>
There	O
are	O
also	O
people	O
who	O
choose	O
to	O
have	O
a	O
password-protected	O
screensaver	B-General_Concept
set	O
to	O
activate	O
after	O
some	O
period	O
of	O
inactivity	O
,	O
thereby	O
requiring	O
the	O
user	O
to	O
re-enter	O
his	O
or	O
her	O
login	B-General_Concept
credentials	O
to	O
unlock	O
the	O
screensaver	B-General_Concept
and	O
gain	O
access	O
to	O
the	O
system	O
.	O
</s>
<s>
The	O
terms	O
became	O
common	O
with	O
the	O
time	B-General_Concept
sharing	I-General_Concept
systems	O
of	O
the	O
1960s	O
and	O
Bulletin	B-Application
Board	I-Application
Systems	I-Application
(	O
BBS	O
)	O
in	O
the	O
1970s	O
.	O
</s>
<s>
Early	O
home	O
computers	O
and	O
personal	B-Device
computers	I-Device
did	O
not	O
generally	O
require	O
them	O
until	O
Windows	B-Device
NT	I-Device
,	O
OS/2	B-Application
and	O
Linux	B-Application
in	O
the	O
1990s	O
.	O
</s>
<s>
The	O
noun	O
login	B-General_Concept
comes	O
from	O
the	O
verb	O
(	O
to	O
)	O
log	O
in	O
and	O
by	O
analogy	O
with	O
the	O
verb	O
to	O
clock	O
in	O
.	O
</s>
<s>
While	O
there	O
is	O
no	O
agreed	O
difference	O
in	O
meaning	O
between	O
the	O
terms	O
login	B-General_Concept
,	O
logon	O
and	O
sign-in	O
,	O
different	O
technical	O
communities	O
tend	O
to	O
prefer	O
one	O
over	O
another	O
–	O
Unix	O
,	O
Novell	O
,	O
Linux	B-Application
and	O
Apple	O
typically	O
use	O
login	B-General_Concept
,	O
and	O
Apple	O
's	O
style	O
guide	O
says	O
"	O
Users	O
log	O
in	O
to	O
a	O
file	O
server	O
(	O
not	O
log	O
on	O
to	O
)	O
...	O
"	O
.	O
</s>
<s>
In	O
the	O
past	O
,	O
Microsoft	O
reserved	O
sign-in	O
to	O
accessing	O
the	O
Internet	O
,	O
but	O
from	O
Windows	B-Application
8	I-Application
onward	O
it	O
has	O
moved	O
to	O
the	O
sign-in	O
terminology	O
for	O
local	O
authentication	O
.	O
</s>
