You can remove the linkback to their site from your footer,
without removing the copyright notice itself.

These are the different variants available to us :
Linked
Search Engine Friendly URLs by vBSEO 3.1.0
Content Relevant URLs by vBSEO 3.1.0
Search Engine Optimization by vBSEO 3.1.0
SEO by vBSEO 3.1.0
Linkback Enabled by vBSEO 3.1.0

Not Linked
Search Engine Friendly URLs by vBSEO 3.1.0 © 2007, Crawlability, Inc.
Content Relevant URLs by vBSEO 3.1.0 © 2007, Crawlability, Inc.
Search Engine Optimization by vBSEO 3.1.0 © 2007, Crawlability, Inc.
SEO by vBSEO 3.1.0 © 2007, Crawlability, Inc.
Linkback Enabled by vBSEO 3.1.0 © 2007, Crawlability, Inc.
(I use the non-linked "SEO by vBSEO 3.1.0 ©2007, Crawlability, Inc." version in the footer in my Forum)


Thanx,
Shadab.