open source licensing

If someone uses the iText library in an android application for PDF without purchasing license, how will iText know he did that? Since he will not be releasing the source code how will they know he used their library? how could they take legal action against him? Again I am not planning in doing this. I was just curious.
Can iText 2.1.7 (MPL/GPL) licence be used in commercial projects? I am not a legal guy but lots of discussion threads suggest that there is no issue using the earlier version (2.1.7) of iText in commercial projects as that version is bounded with terms & conditions governed by MPL /GPL license.