Out of control query

I have an inventory system based on PostgreSQL 8.3.5, JBoss,
Hibernate......

I have a query builder that lets users filter data in a fairly complex way.

For some reason the search gets out of control and consumes all CPU.

I set my statement timeout to 2 minutes and this keeps the system from
going down totally, but this is happening much more frequently than it
used to.

I can find the problem with the individual query easily enough, but I
would like a more general solution.

What seems strange to me is that one one core of my Quad core x5472 is
100%. The others show minimal usage.

I would think that other users would get a different core and one query
could not deadlock the whole system for everyone.

*Do you think this is due to my Postgres or JBoss AS configuration for
database connections?*

Any advice will be greatly appreciated.