Maybe my opponent somehow reached into my machine via the Java applet to crash it and damage it beyond repair.
Can't happen. Java works in a 'sandbox' giving other users or applets little power over files, much less low-level system stuff. The Virtual Machine (VM) only gives a basic type of access to the system where very little damage can be done. Of course, the MicroSoft implementation of the VM has been found to not only be buggy, but a security risk. (Which is why Sun sued them in the first place.)
MicroSoft software, on the other hand, allows plenty of buggy stuff through. Do you use Internet Explorer? Do you always make sure you've
run the updates?
Oh, and look into
Linux.
This happened before I learned about the recent VM (Virtual Machine) exploit and before I had a chance to update my system (I believe I was current with other updates, esp. for Internet Explorer 6). Actually, Yahoo Chess may have been an Active X applet not Java.