link: operator acting strangely, rankings take a dive

link:www.example.com shows results, link:example.com shows zero

[dial_d]

About 10 days ago two of my websites dropped off the map on Google. They have not been banned but instead seem to be penalized because they dropped 100s of positions on almost all keywords. Pages that ranked #1 for months have disappeared into the +500 results range. Even 4 word keyphrases that I am the only one targetting have been affected.

I've really been scratching my head on this one because I do nothing that I consider questionable in terms of SEO practices. Also, I have a small network of related websites but only these two sites have been effected. Even though all of the sites in my network are similar in design and SEO practices.

Earlier today I discovered something that feels like it must be a clue but I'm unsure what to make of it. For my other sites, which haven't suffered a drop in rankings, doing a link:www.domain.com results the exact same results as doing link:domain.com. On the two affected sites link:www.domain.com returns a few results but link:domain.com returns nothing at all!

Anybody got any ideas as to what this could signify?