How to fight website thefts?

Our units conversion website was stolen many times. People simply copied the whole content as it was and placed it elsewhere. Sometimes they kept copyright information intact, sometimes they simply removed it. I never knew how to react. Should I try to complain? But I do not have enough time and money to try to sue them. So I always endured.

Finally there appeared to be a new kind of thief. The new illegal copy of convert-me.com was different. They copied all the content and the conversion programs, they removed all copyright info, but they also changed the look of the pages. The "new" website appears different at first sight, but a closer look reveals all the content being the same.

The bad guys did not stop by having a copy of our site with a new look. They started to promote it, so the site is gaining its audience. The people who visit the illegal copy don't even know it is a copy. The original site has been developed since then, new units were added, some errors were fixed. Of course, the illegal copy is not being developed.

I'm now in doubt what to do. The illegal copy of the site does not even give any contact information. I guess I can only ignore the thieves and hope people could eventually find the original site.

P.S. I intentionally do not give a link to the illegal copy of the site as I don't want to give it extra promotion. However, it's not a secret. I can give a link to those who are interested.

P.P.S. As a proof of authenticity of convert-me.com, here's a link to web archive, showing how our site looked in 2000. And here's a link showing how it looked in 1999 before we moved to convert-me.com domain.