Windows malware may get all the attention, but OS X can be vulnerable too, and if you think your Mac might be infected by something dubious then it’s important to take a closer look.

KnockKnock UI is a tiny free application which lists persistently installed Mac software (modules which are loaded when your system starts), submits them to VirusTotal for checking with 50+ antivirus engines, and reports the results.

Launch KnockKnock UI, click “Start Scan”, and it begins to search for persistent software of various types: “Authorization Plugins”, “Browser Extensions”, “Kernel Extensions”, “Launch Items”, “Library Inserts”, “Login Items” and “Spotlight Importers”.

Your Mac’s startup programs are organised into several categories

Once the scan is complete, an alert tells you the total number of programs found, and how many were flagged as threats by VirusTotal. (Keep in mind that false alarms aren’t unusual; seeing scores like 2/57 or 3/57 doesn’t necessarily mean the file is malware.)

Clicking a category shows you everything KnockKnock UI has uncovered, its location and VirusTotal score, with buttons to display further information about the file (size, created/ modified times, hashes, more) and open its folder.

KnockKnock UI is a long way from a full-strength antivirus tool, but it’s quick, easy to use, and a great way to get a second opinion on your Mac’s security status, and that’s good enough for us.