Some viruses protect themselves by blocking security Web sites, anti-virus programs, and other tools that could be used against them, including Windows' System Configuration utility and Registry Editor. They cleverly block anti virus Web sites by altering your Hosts file, a text file with no extension that individual programs use to assign a specific IP address to a Web page. The Hosts file will be in a different folder depending on your operating system:
Windows XP/7/8 = C:\Windows\system32\drivers\etc Windows 2000/NT = C:\WINNT\system32\drivers\etc Windows 95/98/Me = C:\Windows
To correct the problem, double-click the Hosts file and choose Notepad to open it. Delete any line in the file that refers to an anti virus Web site. Or you can simply delete the Hosts file and Windows will re-create it automatically with zero entries. Now browse to an online virus scanner to check your hard drive and remove the virus.