It happens on a lot of sites
Download the free ClamXav from here and run a scan on your Macintosh HD after updating the definitions, perhaps you have a DNS changer malware.
Did you change your DNS settings to another? Call your ISP and/or get the ISP DNS settings closest to your location and reset them in Network Preferences and/or on your router.
Next see if you are having the problems if the router is bypassed, connect the modem via Ethernet cable and repower the modem to get a new IP from your ISP.
Is your router secure? It might have been hacked. Update it's firmware and secure it just to rule that out.
Open your Terminal program and type
and press enter, the results should look like so
# Host Database
# localhost is used to configure the loopback interface
# when the system is booting. Do not change this entry.
if there is anything after this, your hosts file has been altered and needs to look only like the above.
Use the free TextWrangler to Open File By Name /etc/hosts and make the correction and save with your Admin password.
Next run through thsese if your still having troubles.
Once you've got a clean machine and/or Safari, don't use it on 10.6 anymore.
Safari 6 is only on 10.7/10.8, so 10.6 users should be using Firefox at this point to keep recieving fresh browser security updates.
Not sure what you mean in your last paragraph?
My Safari is 5.1.7.
Looks like ds store has gone off shift, but what I'm sure he meant was that your Safari (along with associated WebKit framework) has over 100 known vulnerabilities that will almost certainly never be patched. Similarly, it's uncertain how much longer OS X 10.6 will receive security updates. Your only recourse is to update to 10.7 / 10.8 or embrace Firefox.