Seeing Pharma Hack persists AFTER update to 4.4.2

One of my sites was hit with what I believe to be a variant of the Pharma Hack while we were using wordpress 4.2.

While other descriptions of this hack have said that it is not visible to the normal visitor, this was visible in the form of words randomly added within the body of our pages such as “viagra,” “cialis,” “ambulance,” “get,” and “prostate” all of which were links to various pharmaceutical purchase websites.

We updated to 4.4.2, updated all of our plugins, and cleaned up the offending code, only to find the same issues back again within a week, and before we could create a backup.

I’ve seen some suggesting that it could come back due to malicious files placed into the Plugins folders, so we checked for that but did not see anything out of the ordinary.

Any advice as to what else we should check on to ensure this does not happen again would be greatly appreciated.

Thank you for any suggestions.