I highly recommend Eli’s Anti-Malware plugin. I’ve been working on this same issue (RevSlider hack that installed malware & backdoors) for 5 days now and his plugin has performed amazingly. I check for his updated definitions via the plugin sidebar a couple times a day and read these forums for his notes.
I tried the free versions of Sucuri and Wordfence, both of which could find some problems. Neither could actually fix them though, at least without subscribing to their services. I kept the free versions installed for the auto-emails on login attempts, file changes and such.
Eli’s plugin was tackling the issue within 30 minutes of installing. He has been constantly updating his malware definitions for the plugin, so it caught a few more smaller issues over the next few days as he improved the plugin’s ability to hunt this bug.
Same RevolutionSlider outdated version bug got 5 of my WordPress sites on a shared host. First notice from my host was on Nov 30th, 2014 that their auto-scan had deleted a suspicious file in the RevSlider directory. I didn’t notice it until Google blocked two of my sites in mid-December.
I was relying on my hosts free backup service, but it didn’t have a backup from before the first notice of a problem. So I’ve been working without a net, unable to go back to a truly clean version of these WordPress installs.
Nearly had to tell my wife we had lost her online store for the holiday season. Thanks to Eli, we’re up and running. Plus keeping an eye out for any more of his updates.