I log off my account and went in on a newly created account and same problem. I also know is not my router because all my other equipment is working properly. (mac desktop, mac laptop and Itouch) I also just installed CLAMXAV software and it found no infected files. I am runing a scan again just to be sure.
You could try:
1 - disable all virus software
2 - relax all firewall restrictions
3 - remove all browser security, especially fraudulent sites etc
4 - disable all third party utilities
5 - flush DNS cache
6 - repair disk and permissions
7 - restart
If this does not work it may be time to backup the disk and do a clean install.