You may want to look over your UBB.threads license before removing such notices. Here is a portion of the license that applies to your question:
[]You may not alter or remove any copyright and other proprietary notices or legends of Infopop or its suppliers (including the "Powered By" legend appearing in the HTML title) that are contained in the Software, within the scripts and HTML generated by the scripts, and related documentation as delivered under this License. All such notices or legends remain readily perceptible to the human eye.
Related link:
http://www.infopop.com/products/ubbthreads/license.html In short:
Don't remove it.