order with connection on an account of s'one else !!

hi everyone
i discovered a problem these weeks : several customers succeeded in ordering without create any account since they had been connected on another account (without knowing it).
Each one lives far from the real owners of the incriminated accounts (which exclude a cyber-cafe connection) and fact interesting, each of the 3 accounts used were created the same day of the problem and about only 2 hours before in one case.
How is it possible ?
Have you ever noticed something like this and how to fix it?

i'm quite late in my upgrade and am still on 1.2.5 version

thanks by advance

Do a advanced search on "Sessions" in the Customers and Order section.

thanks tophand for your reply, but i don't see what i can do and what this search for ?
please tell me more

Your cart is not handling sessions correctly. By doing a search, you will find threads (in Customers and Orders sub forum) that could help you with your problem.
The very best fix is that you upgrade your cart.

M