enigma1 - 2:19 pm on Dec 2, 2011 (gmt 0)

I uploaded one of the articles on my website using CSE HTML Validator.

That is strange, if you publish articles I would expect to use some web application blog, cms etc, which would include storing content in a database and a content editor. And of course the moment you edit the article (even to setup the published date) you would see the problem or at least once you save the content the editor will convert the text and a search will reveal what happened.

I don't know of the particular package you used and whether or not the thief knew in advance how you will publish documents and how you will search/verify them. It's possible they got a hint on how you were going to verify them.