Free Anti Spam Software

now i need a anti spam software,please tell me where do i can download a free anti spam software?

Instead of opening my browser to my homepage, http://www.yahoo.com, some kind of malicious software is changing my homepage to http://www.atotalsafety.com, and I am getting constant pop-up messages which try to get me to download security software (anti-spy, anti-adware, scans for spyware, spam protection, etc.). I have a very recent version of Norton Antivirus software installed and running, as well as the malicious software detection tool from Microsoft, but neither program is able to detect this malicious software described above. Has anyone else encountered this problem, and if so, how can it be resolved?