A quick note on Mac malware

The most recent bit of OS X malware making the rounds is a fake file converter program that installs a PHP backdoor accessible via Tor, allowing some rando to rummage around on your machine. As is usual, you, the victim, have to download the software, and run it, and allow the program to install its backdoor code.

If you want to protect yourself from malware on your Mac, there are three principal things you can do.

  1. Don’t download software if you’re not 100% sure of its provenance, function, and dependability. Just because it’s on MacUpdate doesn’t mean it’s okay.
  2. If you do accidentally download something – say you’re using one of those dodgy file-sharing sites with fifteen ads masquerading as the real download button – don’t run it. Just delete it.
  3. If, despite all this, you did download something and run it, under no circumstances enter your administrator password when it asks to install “support software” or the like unless you know exactly what’s going to happen if you do.

You still have the backstop that nothing is going to get installed as a persistent backdoor if you don’t enter your administrator password when prompted, but it’s trivially easy to build a backdoor that runs only when the software is running. Don’t run random programs you aren’t sure you can trust. Find a trusted third party that knows for certain that the program is safe.

If you insist on living dangerously, there are a couple utilities I’ll mention below that will allow you to try to prevent the damage, and I emphasize try. They are no guarantee of safety; if you download pirated software or random things to “try them out” or “see if they work”, you’re sooner or later going to mess yourself up. These monitors are counting on your personal software sophistication to protect yourself from harm. They are only useful if you understand what they are telling you.

I run the programs I mention below not because they magically keep me safe from bad programs, but because I like to know what’s going on behind the scenes on my Mac. If you aren’t certain you know what ~/Library/LaunchAgents does, or what a connection over port 443 means, you may not want to try using these programs, because they will confuse you; if you try to use them by simply blocking everything, you’ll find that things that are actually supposed to make outgoing connections (like Mail) will stop working, and that software that really needs to install agents, like Dropbox, will break. Conversely, if you just say “yes” to everything, things like the fake file converter mentioned above will get to install their hooks and they will allow who knows who to read your mail and download your naked selfies.

If I haven’t lost you at this point – you understand OS x/Unix well enough to understand what connections are good and what ones are bad, and you know what a file in ~/Library/LaunchAgents is for:

  • Little Snitch is a program that sits in the background and alerts you whenever your machine tries to make a network connection, whether incoming our outgoing. If you don’t respond, the connection is automatically blocked. You can add rules to automatically allow or automatically block connections. This utility will let you know if someone is actively trying to connect to your machine, or if your machine is trying to make an unexpected outgoing connection.
  • BlockBlock is a utility that monitors attempts to install long-running processes like the one that constitutes the Tor/PHP backdoor and reports them to you with the option to block them. In the case of EasyDoc Converter, it’d be pretty easy to spot that the software was up to no good, as it’s attempting to install stuff named “dropbox” in an attempt to hide their nasty software as part of good software.

As helpful and useful as these monitors are – I run them, and I like them – they’re still not going to 100% protect you from what happens if you run random things you download from the Internet, especially if you say “sure, why not?” when they ask for your administrator password.

Just avoid the off-the-wall random links and wait until someone reputable has said, “yeah, that’s good” before trying it.

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