The most likely reason that defcon has the most dupes is because it occurs after blackhat.
Cons Duplicates Talks
  • DEF CON-18 - Las Vegas, USA
          Total Talks : 157
25
  • DEF CON-17 - Las Vegas, USA
          Total Talks : 149
24
  • DEF CON-15 - Las Vegas, USA
          Total Talks : 121
23
  • DEF CON-16 - Las Vegas, USA
          Total Talks : 121
19
  • SecTor-2010 - Canada
          Total Talks : 51
11
  • DEF CON-12 - Las Vegas, USA
          Total Talks : 75
10
  • DEF CON-13 - Las Vegas, USA
          Total Talks : 80
  • Blackhat USA-2008 - Las Vegas, USA
          Total Talks : 86
  • BruCON-2010 - Brussels, Belgium
          Total Talks : 31
9
  • Blackhat USA-2010 - Las Vegas, USA
          Total Talks : 99
  • OWASP Appsec-2010 - Washington DC, USA
          Total Talks : 65
8
  • Chaos Communication Congress-23 - Berlin, Germany
          Total Talks : 133
7
  • DEF CON-10 - Las Vegas, USA
          Total Talks : 69
  • Berlinsides-2010 - Berlin, Germany
          Total Talks : 30
  • Chaos Communication Congress-25 - Berlin, Germany
          Total Talks : 82
  • NinjaCon-2010 - Vienna, Austria
          Total Talks : 40
  • SyScan-2010 - Singapore
          Total Talks : 15
6
  • DEF CON-08 - Las Vegas, USA
          Total Talks : 48
  • Blackhat USA-2005 - Las Vegas, USA
          Total Talks : 106
  • Blackhat USA-2007 - Las Vegas, USA
          Total Talks : 97
  • Blackhat USA-2009 - Las Vegas, USA
          Total Talks : 72
  • Chaos Communication Congress-22 - Berlin, Germany
          Total Talks : 125
  • SyScan-2009 - Taipei, Taiwan
          Total Talks : 10
  • The Fifth HOPE -2004 - USA
          Total Talks : 67
  • HOPE Number 6-2006 - USA
          Total Talks : 73
  • HITBSecConf Malaysia-2010 - Kuala Lampur, Malaysia
          Total Talks : 21
  • SOURCE Boston-2010 - Boston, USA
          Total Talks : 48
  • Ruxcon-2012 - Melbourne, Australia
          Total Talks : 28
5
  • Blackhat USA-2003 - Las Vegas, USA
          Total Talks : 35
  • Blackhat USA-2004 - Las Vegas, USA
          Total Talks : 58
  • DEF CON-14 - Las Vegas, USA
          Total Talks : 83
  • ITWeb Security Summit-2010 - Johannesburg, South Africa
          Total Talks : 42
  • LASCON-2010 - Austin, USA
          Total Talks : 16
  • OWASP Appsec-2009 - Washington DC, USA
          Total Talks : 64
  • TROOPERS-2008 - Munich, German
          Total Talks : 26
  • SyScan-2005 - Singapore
          Total Talks : 20
  • SyScan-2009 - Hong Kong, China
          Total Talks : 9
  • The Last HOPE-2008 - USA
          Total Talks : 96
  • Blackhat Europe-2004 - Amsterdam, The Netherlands
          Total Talks : 22
  • SOURCE Boston-2009 - Boston, USA
          Total Talks : 42
  • SecTor-2009 - Canada
          Total Talks : 24
  • SecTor-2007 - Canada
          Total Talks : 24
  • ekoparty-2010 - Buenos Aires, Argentina
          Total Talks : 23
  • BlueHat-2008 - Redmond, USA
          Total Talks : 21
4
  • DEF CON-09 - Las Vegas, USA
          Total Talks : 54
  • Chaos Communication Congress-27 - Berlin, Germany
          Total Talks : 90
  • HITBSecConf Amsterdam-2010 - Amsterdam, The Netherlands
          Total Talks : 26
  • OWASP Appsec-2010 - USA
          Total Talks : 17
  • Chaos Communication Congress-24 - Berlin, Germany
          Total Talks : 94
  • SOURCE Barcelona-2010 - Barcelona, Spain
          Total Talks : 18
  • CarolinaCon-5 - Raleigh, USA
          Total Talks : 10
  • SyScan-2010 - HangZhou, China
          Total Talks : 11
  • Blackhat Europe-2008 - Amsterdam, The Netherlands
          Total Talks : 23
  • Blackhat Europe-2005 - Amsterdam, The Netherlands
          Total Talks : 25
  • SecTor-2008 - Canada
          Total Talks : 24
  • LayerOne-2008 - Anaheim, USA
          Total Talks : 11
  • CONFidence -2008 - Krakow, Poland
          Total Talks : 15
  • ekoparty-2009 - Buenos Aires, Argentina
          Total Talks : 12
  • ShakaCon-5 - Honolulu, USA
          Total Talks : 20
  • Positive Hack Days-2012 - Moscow, Russia
          Total Talks : 42
  • Breakpoint-2012 - Melbourne,Australia
          Total Talks : 14
3
  • Blackhat Asia-2002 - Tokyo, Japan
          Total Talks : 19
  • THOTCON-1 - Chicago, USA
          Total Talks : 12
  • OWASP Dublin-2010 - Ireland
          Total Talks : 17
  • OWASP AppSec Brasil-2010 - Brazil
          Total Talks : 14
  • OWASP IBWAS-2010 - Portugal
          Total Talks : 20
  • hashdays-2010 - Lucerne, Switzerland
          Total Talks : 14
  • Chaos Communication Congress-17 - Berlin, Germany
          Total Talks : 34
  • Chaos Communication Congress-19 - Berlin, Germany
          Total Talks : 70
  • Chaos Communication Congress-26 - Berlin, Germany
          Total Talks : 77
  • ShmooCon-2005 - Washington DC, USA
          Total Talks : 35
  • BruCON-2009 - Brussels, Belgium
          Total Talks : 24
  • SOURCE Barcelona-2009 - Barcelona, Spain
          Total Talks : 17
  • SyScan-2006 - Singapore
          Total Talks : 17
  • SyScan-2007 - Singapore
          Total Talks : 17
  • SyScan-2008 - Taipei, Taiwan
          Total Talks : 12
  • 18th USENIX Security Symposium-2009 - Montreal, Canada
          Total Talks : 45
  • Blackhat Europe-2009 - Barcelona, Spain
          Total Talks : 24
  • Blackhat Europe-2006 - Amsterdam, The Netherlands
          Total Talks : 25
  • HITBSecConf Malaysia-2009 - Kuala Lampur, Malaysia
          Total Talks : 19
  • OWASP FROC-2010 - Denver, USA
          Total Talks : 20
  • KiwiCon-2010 - Wellington, New Zealand
          Total Talks : 25
  • BlueHat-2010 - Redmond, USA
          Total Talks : 17
  • LayerOne-2005 - Anaheim, USA
          Total Talks : 12
  • ekoparty-2007 - Buenos Aires, Argentina
          Total Talks : 13
  • BlueHat-2009 - Redmond, USA
          Total Talks : 14
  • BlueHat-2006 - Redmond, USA
          Total Talks : 11
  • CanSecWest-2011 - Vancouver, Canada
          Total Talks : 17
  • Notacon-8 - Cleveland, USA
          Total Talks : 39
  • HITBSecConf Malaysia-2012 - KL, Malaysia
          Total Talks : 34
2
  • ShmooCon-2011 - Washington DC, USA
          Total Talks : 49
  • Blackhat USA-1999 - Las Vegas, USA
          Total Talks : 33
  • Blackhat USA-2000 - Las Vegas, USA
          Total Talks : 5
  • Blackhat USA-2001 - Las Vegas, USA
          Total Talks : 38
  • Blackhat Asia-2002 - Tokyo, Japan
          Total Talks : 12
  • Blackhat DC-2003 - DC, USA
          Total Talks : 1
  • TROOPERS-2010 - Heidelberg, Germany
          Total Talks : 21
  • DEF CON-11 - Las Vegas, USA
          Total Talks : 65
  • Hackito Ergo Sum-2010 - Paris, France
          Total Talks : 16
  • Notacon-7 - Cleveland, USA
          Total Talks : 36
  • House Con-2010 - USA
          Total Talks : 9
  • QuahogCon-2010 - USA
          Total Talks : 22
  • OWASP Day Mexico-2010 - Mexico
          Total Talks : 8
  • OWASP BASC-2010 - Boston, USA
          Total Talks : 12
  • OWASP BeNelux-2010 - Netherlands
          Total Talks : 9
  • Chaos Communication Congress-18 - Berlin, Germany
          Total Talks : 65
  • Chaos Communication Congress-21 - Berlin, Germany
          Total Talks : 148
  • OWASP Appsec-2010 - Stocholm, Sweden
          Total Talks : 36
  • BugCon-2010 - Mexico
          Total Talks : 56
  • ShmooCon-2006 - Washington DC, USA
          Total Talks : 35
  • ShmooCon-2007 - Washington DC, USA
          Total Talks : 37
  • AthCon-2010 - Athens, Greece
          Total Talks : 18
  • SyScan-2004 - Singapore
          Total Talks : 16
  • SyScan-2008 - Hong Kong, China
          Total Talks : 8
  • SyScan-2009 - Singapore
          Total Talks : 15
  • 13th USENIX Security Symposium-2004 - San Diego, USA
          Total Talks : 41
  • 17th USENIX Security Symposium-2008 - San Jose, USA
          Total Talks : 47
  • Blackhat Europe-2010 - Barcelona, Spain
          Total Talks : 31
  • Blackhat Europe-2007 - Amsterdam, The Netherlands
          Total Talks : 25
  • 4th USENIX Workshop on Offensive Technologies -2010 - Washington DC, USA
          Total Talks : 12
  • HITBSecConf Malaysia-2006 - Kuala Lampur, Malaysia
          Total Talks : 26
  • HITBSecConf Malaysia-2008 - Kuala Lampur, Malaysia
          Total Talks : 28
  • SOURCE Boston-2008 - Boston, USA
          Total Talks : 27
  • PacSec-2010 - Tokyo, Japan
          Total Talks : 10
  • LayerOne-2007 - Anaheim, USA
          Total Talks : 11
  • LayerOne-2006 - Anaheim, USA
          Total Talks : 11
  • KiwiCon-2008 - Wellington, New Zealand
          Total Talks : 21
  • CONFidence -2006 - Krakow, Poland
          Total Talks : 16
  • t2-2008 - Helsinki, Finland
          Total Talks : 11
  • t2-2009 - Helsinki, Finland
          Total Talks : 14
  • PacSec -2005 - Tokyo, Japan
          Total Talks : 11
  • BlueHat-2007 - Redmond, USA
          Total Talks : 18
  • Notacon-5 - Cleveland, USA
          Total Talks : 32
  • Notacon-6 - Cleveland, USA
          Total Talks : 32
  • Security B-Sides San Francisco-2011 - San Francisco, USA
          Total Talks : 27
  • Hackito Ergo Sum-2011 - Paris, France
          Total Talks : 16
  • Infiltrate-2011 - Miami, USA
          Total Talks : 14
  • TROOPERS-2011 - Heidelberg, Germany
          Total Talks : 22
  • Thotcon-2012 - Chicago, USA
          Total Talks : 18
  • Deepsec-2012 - Vienna, Austria
          Total Talks : 40
  • CircleCityCon-2014 - Indianapolis,usa
          Total Talks : 37
1
Cons Total Duplicates Talks
DEF CON 129
Blackhat USA 27
Chaos Communication Congress 24
SyScan 21
SecTor 18
OWASP Appsec 16
BruCON 11
Blackhat Europe 10
SOURCE Boston 10
ekoparty 9
HITBSecConf Malaysia 8
BlueHat 7
Berlinsides 6
LayerOne 6
NinjaCon 6
HOPE Number 6 5
The Fifth HOPE 5
SOURCE Barcelona 5
Ruxcon 5
TROOPERS 5
LASCON 4
CONFidence 4
The Last HOPE 4
ITWeb Security Summit 4
ShakaCon 3
CarolinaCon 3
Positive Hack Days 3
Blackhat Asia 3
Breakpoint 3
HITBSecConf Amsterdam 3
ShmooCon 3
KiwiCon 3
Notacon 3
THOTCON 2
OWASP Dublin 2
hashdays 2
OWASP FROC 2
CanSecWest 2
OWASP IBWAS 2
OWASP AppSec Brasil 2
18th USENIX Security Symposium 2
House Con 1
OWASP Day Mexico 1
13th USENIX Security Symposium 1
17th USENIX Security Symposium 1
Deepsec 1
BugCon 1
Blackhat DC 1
Thotcon 1
PacSec 1
Security B-Sides San Francisco 1
Infiltrate 1
QuahogCon 1
4th USENIX Workshop on Offensive Technologies 1
AthCon 1
t2 1
Hackito Ergo Sum 1
OWASP BeNelux 1
OWASP BASC 1
CircleCityCon 1