Thanks for your help. By reading the thread it only mentions for a misleading warning which is not actually the case. While all the signatures are up-to-date, new versioned software usually fixes mistakes on old versions and/or adds new features etc.
In the case of ClamAV, since in the official site there is a new release which they claim is in Ubuntu backports repository and it not, there should be a way of upgrading to the latest version.
If anyone has figured this out please share it.