How to bypass duplicate content from nonexistent variables

[Unce]

There is situation, when many different URLs on same domain have same content. Basically it's because of variables. I have noticed, that many sites have this problem. For example:

http://www.example.com/ and
http://www.example.com/?lang="lv"

have same content.

What if someone puts link on http://www.example.com/?lang="lv". Should they use mod_rewrite to solve this problem?

[edited by: tedster at 4:46 pm (utc) on May 11, 2008]
[edit reason] use example.com [/edit]

[fishfinger]

I take it that lv is the default langauge option and the urls are being displayed when people or spiders come BACK to it from another language.

As it's dynamic you could
(a) nofollow the link to the default English language option
(b) also autogenerate a noindex,nofollow tag for this page

But, yes, a rule in htaccess will make absolutely sure you don't waste any IBLs.

[Unce]

Actually, any URL like
http://www.example.com/ and
http://www.example.com/?lang="lv"
http://www.example.com/?id="3"
will have same content, because these variables are not defined. This could be tested on any site for example: www.webmasterworld.com/?id=7
The question is, should it be so?

[edited by: Unce at 6:35 pm (utc) on May 11, 2008]

[fishfinger]

Sorry, I overlooked title of your post which does make that clear. I've read that this is a potential way for negative SEO to hurt your site, but not any accounts of people who have suffered as a result of it.

If you're concerned about malicious IBLs to non-existent urls then the answer is still yes - the re-writes will fix that too. I believe you can also get these to return a 404.

How much of a risk this sort of thing is in teh first place I don't know.

[g1smd]

See this thread from yesterday: [webmasterworld.com...]