It soon won't matter; in the past a hyphen was better than an underscore, it seems it will no longer make a difference. The problem you're experiencing is unrelated to the use of underscores or hyphens.
Exactly. G Bot is getting more intelligent everyday and removing the un-necessary difference between such thing. But somehow, I still like hyphen over underscore
The most closely held SEO secret (until now that is) is to use both....i.e. www.mydomain.com/computers_-internet/ and for slightly higher rankings...www.mydomain.com/computers-_internet/ And thus another SEO urban legend is born. Disclamer: Intended for humor purposes only, do not try at home. Besides, it makes for incredibly ugly urls.
I was looking at this underscore thing pretty negatively because of my SEO site, I have just realized that my directory uses them so I am 50/50 about it now.
Just remember to heed MC's words when he said Google don't penalize for using hyphens or 'dashes' in an url but they don't speak for other search engines.
you do realise that once you change the structure an urls, All your internal TBPR , for the changed urls, will vanish