So this has come up a couple of times recently, so after some research I thought I'd share the news.

In 7.4, built-in support for ClamAV has been removed, and Liferay has no current plans on restoring that functionality.

If you have upgraded from a previous version and you were using ClamAV, you may not be aware that your antivirus scanning actually has not been happening as there is nothing in CE 7.4 to tell you that there are no instances of com.liferay.document.library.kernel.antivirus.AntivirusScanner available to actually perform the virus scanning.

If you want or need virus scanning in CE 7.4, your only option at the moment is to roll your own implementation of AntivirusScanner and implement the functionality yourself.

The only guidance I can give you here is to look towards the CE 7.3 implementation code as it can help frame how you need to build the implementation.