IBM have securities options that are famous. I see you found out why
That is why they are so popular in corporate enviroments. It is very posible that you had that password from before. Did you buy the PC used?
Probably something was skipping the password, and that is no longer active. They usually have s jumper, but it might not be so obvious since they want to hide it. If you forget your thinkpad password you have to send the laptop to IBM.
Unplug the power cable, remove the batery, try to switch the PC on, both from the button at the front and from the button in the power supply (if it has) then leave it withouth the batery for 10, or more minutes. Relax, watch The simpsoms, then re-insert the batery, and try again