Thank you LOTR. The iAntiVirus has an uninstaller but the ClamXav.app I couldn't find if it had it. I already went to Preferences and have deleted the two files with iAntiVirus I found but could only find one with ClamXav on it. I just want to make sure I got rid of them all. What's the name of the application you said can show hidden files. Is it safe to have and use it. Thanks.

By the way. I have now bought a VirusBarrier X6 from Apple but my problem still hasn't improve at all - the hacker still creating havoc in my computer. I am so frustrated, I don't know how to get rid of the hacker in my mac. Hope you could help me more. Many thanks.