Do you have Earthlink Highspeed? They updated their DNS awhile back to give back a custom Earthlink/Yahoo seach page for non-existant domains.
Normally this would not be a problem- but for some it can. For me it was. The AT&T network client my company uses for VPN does not act well when DNS is hijacked that way.
Earthlink has what they are calling “Opt-Out DNS”. Update your router or DNS entries to include the following DNS servers: 207.69.188.172 and 207.69.188.171.
Details can be found here: http://kb.earthlink.net/case.asp?article=187117