The only reason to ever put antivirus on a Linux / UNIX machine is if you are using it to protect other operating systems (read: Microsoft Windows).
If you insist, however, then most everybody uses the free clamav product anyway - although I'm sure you can easily find other companies selling AV product for Linux (mostly targeted at n00bs who don't realize they don't need it).
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Use freshclam command that will update your anti virus
For scanning the directories [/home/xxxx/public_html]# clamscan -ir
will give you out put like
home/xxxx/public_html/index.htm: Exploit.HTML.IFrame-6 FOUND
/home/xxxx/public_html/main.htm: Exploit.HTML.IFrame-6 FOUND
Rather than install the rpms manually by downloading them, I would enter the repository into your yum configuration, then as they get updated upstream, you'll be able to just yum upgrade inline with your upgrade policy, if you have one.
I realise that most people on here are, like myself, fans of the command line but in my experience most people who ask about CentOS are using WHM/Cpanel to manage it.... especially when they don't know how to manage the security issues.
If this is the case, just go to "Manage Plugins" in your WHM panel and install clamav in a few clicks
Alternatively, consider getting a professional to check over your install.