I do need your help

Hi, guys
For some reason, the homepage of IE was changed by a website. I used to set the homepage of IE as "yahoo". Since yesterday a website set its as the homepage of IE. Though I tried timelessly intending to reset the homepage as "yahoo"again in "internet option, tool", each time I open IE, that website appears again.
Can anyone help me solving this problem ? It's very frustrating as that website links a groups of websites.
I appreciate your help.