If you are like most people it is a password that you reused. I posted a long list of passwords that people had discovered worked a while ago. Here it is again:
First iTunes account password (40 different users)
Old iTunes account password, but not the oldest one
Password used for almost all accounts (3 different users)
All digit Password created a long time ago
Computer/laptop login password (4 users)
Laptop password (2 users)
Computer password (4 users)
Email password (3 users)
iTunes with no capital letters
Password not used anywhere else
All numeric used in the past
Password for old gaming site
PC password (5 users)
“iphonelogin”
work computer password
Current app store password (2 users)
Paypal account password
iPad unlock passcode
Strongest variation of the base password I have ever used
Old password
Old work password
Macbook password (2 users)
Restriction passcode
Gmail password (2 users)
Current Apple ID password (2 users)
Apple MobileMe password
Apple ID password, but all lower case (8 users)
Apple ID password, first one ever used, but all lower case (2 users)
iPhone passcode when corporate profile was installed
Passcode for a website
iPhone screen unlock passcode (9 users)
iPhone unlock passcode at the time the first backup was made (3 users)
First password for work computer
Old password used over 2 years ago (2 users)
Previous owner’s iTunes password
Current laptop password
Wireless network password
Electric bill and Skype password
icloud password, all lower case
Windows login for very old laptop
iMac password (3 users)
First iPhone 4 digit passcode
iTunes password from last year
4 year old password
iTunes password (current) (3 users)
Old PC password
Password for “Good” application
Password used for everything+1234
1234 (4 users)
12345 (2 users)
0000
Password I use for everything else (2 users)
One of my husband’s passwords
Some old non-Apple product password
Screen passcode of the first iPhone that was backed up (2 users)
Old password with different case on first letter
“password”
Windows Administrator password (2 users)
Original Windows Administrator password
Mackbook administrator password
“iphone”+4 digit unlock code
Voicemail password
asd
“herpderp”
“darwin” (first name from credit card account)
First name, all lower case
Ms Exchange account password
Facebook password
Browser password
Network admin password
61 page thread p 14 https://discussions.apple.com/thread/3091672?start=195&tstart=0