Here's yet another reason your SSN is not safe: using statistical analysis and math, it is apparently pretty easy to guess if someone knows your date of birth and your place of birth.
It is sad that it is illegal to use your SSN for any sort of identification purposes, yet, despite that, it is basically universally used for it anyway.
Truly, what we need is an ID system based on biometric data. Though I wonder how that would work for online transactions, where it would be easy enough to send fake parameters instead of your own.
I already knew there were reasons not to share things like your birthday and even place of birth - which is why I generally counsel not to use your real birthday for things online unless you are legally required to. I certainly never do. So here's one more reason not to.
4 years ago