>How I understand it, the TIOBE index only ranks according to hits on search engines and popular Websites. So it cannot really discriminate the context in which the language is being mentioned, or if that is someone actually using that language or only talks about it. Of course there is a certain tendency when a language is mentioned often on forums, which may indicate that these developers are using the language in one way or another. On the other hand, a language I use less often may result in more questions being asked online, as opposed to a language I am using full time for many years.

Yes, that would be correct. However, nowadays, search engines metrics seem to reflect a very close view of what the reality is actually. There could be also an increase in the search results based on tendencies of the market, such as a major release of a product, doubts about the product continuity support. Those can influce the metrics.

>If you would search for "VB.NET is dying", is this a hit, and raises the index of VB.NET? Or do certain companies publish pages with keywords in order to manipulate those rankings?

Yes, that would fall in the above example of doubts over a certain product.

Thanks