Last time I used it a few years ago it was the last four digits of my social security number and my birthyear. Don't remember if it was 8 or 6 digits, try the year written both ways.

Example

1x1-12-5121 is a fake social security number, 1943 is your birth year..

512143 or 51211943.

I just logged into mine using last 4 of my social and my entire birth year.