Something strange with Yahoo Chat

On occasion when I log into Yahoo email chat will open briefly then a window opens telling me I've been disconnected from chat because I've logged on using another computer.

Are they trying to say I'm logged in at that same time on some other computer?

Sometimes I had just previously been logged into Yahoo email on another computer, but always had logged out of Yahoo on that machine before I log in
on my personal computer (the other one is the work intranet machine and won't open chat because of company blocking).

Sometimes it will work after I close Yahoo and log in again.

I'm wondering if someone has hacked into my email?

Thanks!

Yep. Message means a second, more recent logon with your username/password was detected. The most recent logon attempt wins the right to stay logged on

Hmmm, that's what I was afraid of.

Only other person knows my login is my wife and I checked with her - she wasn't on.
So that must mean I've been hacked somehow.

Guess it's time to change passwords!