Dynamic (?) URLs causing duplicate content penalty?

multiple G listings for same content

[ga_ga]

I'm working on a page for somebody at the moment, which appears to have possibly been assigned a pagerank 0 penalty - it was PR4 before the last update with around 30 good quality on-topic backlinks.

Doing a

site:www.domain.com "+www.domain.+com"

search showed up 3 listings:

www.domain.com/
www.domain.com/?source=CompletelyDifferentDomain1.com
www.domain.com/?source=CompletelyDifferentDomain2.com

All 3 listings lead to exactly the same content.

Is it possible Google has followed these URLs from links on other sites (CompletelyDifferentDomain1,2... etc), and, finding itself served with content, has gone ahead & indexed each URL separately, leading to a duplicate content penalty?

Is this possibly something set up by a previous designer, that has backfired?

<edit reason = found more detail>

Discovered the source of these listings - previous designer appears to have added his URL to 2 'list your site' directory type pages - these pages are showing the root URL with query strings attached as above. Is this something worth worrying about or should Google's multiple listing of the same content under different query string URLs not be a problem?

</edit>

[ga_ga]

Possibly a problem related to the fact that it's a query string without a filename?

[jomaxx]

The duplicate page filter is not a penalty - they just don't want numerous mirror pages to all have separate listings. In that particular case, it may take a couple of indexing cycles before Google sees that the pages are identical and merges them. This is a normal situation and I don't see why your PR would be affected at all.

Is this a re-registered domain that had some PR when it was taken over? A lot of people who have scooped up expired domains have been complaining recently about their old, and even some new, links being invalidated.

[ga_ga]

I'll check into that with the owner thanks jomaxx, there's certainly a possibility that could be the case I guess. I can't really check the backlinks easily at the moment because it's currently a PR0, but there seem to be quite a few references listed if I search on "domain.+com". Guess that doesn't really tell me if Google's actually aware of the links though.