<s>
FastTrack	B-Protocol
is	O
a	O
peer-to-peer	O
(	O
P2P	O
)	O
protocol	O
that	O
was	O
used	O
by	O
the	O
Kazaa	B-Protocol
,	O
Grokster	B-Protocol
,	O
iMesh	B-Protocol
and	O
Morpheus	B-Protocol
file	O
sharing	O
programs	O
.	O
</s>
<s>
FastTrack	B-Protocol
was	O
the	O
most	O
popular	O
file	O
sharing	O
network	O
in	O
2003	O
,	O
and	O
used	O
mainly	O
for	O
the	O
exchange	O
of	O
music	O
mp3	B-Application
files	I-Application
.	O
</s>
<s>
The	O
network	O
had	O
approximately	O
2.4	O
million	O
concurrent	B-License
users	I-License
in	O
2003	O
.	O
</s>
<s>
It	O
is	O
estimated	O
that	O
the	O
total	O
number	O
of	O
users	O
was	O
greater	O
than	O
that	O
of	O
Napster	B-Application
at	O
its	O
peak	O
.	O
</s>
<s>
The	O
FastTrack	B-Protocol
protocol	O
and	O
Kazaa	B-Protocol
were	O
created	O
and	O
developed	O
by	O
Estonian	O
programmers	B-Application
of	O
BlueMoon	O
Interactive	O
headed	O
by	O
Jaan	O
Tallinn	O
,	O
the	O
same	O
team	O
that	O
later	O
created	O
Skype	B-Application
.	O
</s>
<s>
It	O
appeared	O
during	O
the	O
end	O
of	O
the	O
first	O
generation	O
of	O
P2P	O
networks	O
Napster	B-Application
shut	O
down	O
in	O
July	O
of	O
that	O
year	O
.	O
</s>
<s>
There	O
are	O
three	O
FastTrack-based	O
networks	O
,	O
and	O
they	O
use	O
mutually	O
incompatible	B-Application
versions	O
of	O
the	O
protocol	O
.	O
</s>
<s>
The	O
most	O
popular	O
clients	B-Protocol
on	O
each	O
are	O
Kazaa	B-Protocol
(	O
and	O
its	O
variations	O
)	O
,	O
Grokster	B-Protocol
,	O
and	O
iMesh	B-Protocol
.	O
</s>
<s>
For	O
more	O
information	O
about	O
the	O
various	O
lawsuits	O
surrounding	O
Kazaa	B-Protocol
and	O
Sharman	B-Protocol
Networks	I-Protocol
,	O
see	O
Kazaa	B-Protocol
.	O
</s>
<s>
FastTrack	B-Protocol
uses	O
supernodes	B-Protocol
to	O
improve	O
scalability	B-Architecture
.	O
</s>
<s>
To	O
allow	O
downloading	O
from	O
multiple	O
sources	O
,	O
FastTrack	B-Protocol
employs	O
the	O
UUHash	B-Algorithm
hashing	B-Error_Name
algorithm	I-Error_Name
.	O
</s>
<s>
While	O
UUHash	B-Algorithm
allows	O
very	O
large	O
files	B-Operating_System
to	O
be	O
checksummed	O
in	O
a	O
short	O
time	O
,	O
even	O
on	O
slow	O
weak	O
computers	O
,	O
it	O
also	O
allows	O
for	O
massive	O
corruption	O
of	O
a	O
file	O
to	O
go	O
unnoticed	O
.	O
</s>
<s>
Many	O
people	O
,	O
as	O
well	O
as	O
the	O
RIAA	O
,	O
have	O
exploited	O
this	O
vulnerability	O
to	O
spread	O
corrupt	O
and	O
fake	O
files	B-Operating_System
on	O
the	O
network	O
.	O
</s>
<s>
The	O
FastTrack	B-Protocol
protocol	O
uses	O
encryption	O
and	O
was	O
not	O
documented	O
by	O
its	O
creators	O
.	O
</s>
<s>
The	O
first	O
clients	B-Protocol
were	O
all	O
closed	B-Application
source	I-Application
software	I-Application
.	O
</s>
<s>
However	O
,	O
initialization	O
data	O
for	O
the	O
encryption	O
algorithms	O
is	O
sent	O
in	O
the	O
clear	O
and	O
no	O
public	B-Application
key	I-Application
encryption	I-Application
is	O
used	O
,	O
so	O
reverse	O
engineering	O
was	O
made	O
comparatively	O
easy	O
.	O
</s>
<s>
In	O
2003	O
,	O
open	B-License
source	I-License
programmers	B-Application
succeeded	O
in	O
reverse-engineering	O
the	O
portion	O
of	O
the	O
protocol	O
dealing	O
with	O
client-supernode	O
communication	O
,	O
but	O
the	O
supernode-supernode	O
communication	O
protocol	O
remains	O
largely	O
unknown	O
.	O
</s>
<s>
The	O
following	O
programs	O
are	O
or	O
have	O
been	O
FastTrack	B-Protocol
clients	B-Protocol
:	O
</s>
