Google-owned VirusTotal starts analyzing Mac malware in a sandbox

The service now extracts behavioral information from scanned Mac executable files

VirusTotal, the most widely used online file-scanning service, is now executing suspicious Mac apps submitted by users inside a sandbox to generate information that could improve the analysis and detection of Mac malware.

This comes at a time when, according to security vendors, the number of potentially unwanted Mac OS X applications, especially adware programs, is at an all time high.

VirusTotal, a Google-owned service, allows users to upload suspicious files and scan them with 54 different antivirus products. However, its scan results are not perfect and should not be taken as guarantees that files are safe.

For many years, the service only performed a static scan of user-submitted files without executing them and this left out an important component of modern malware testing -- behavioral analysis.

Many antivirus products might not detect a file as malicious if it's simply stored on disk, especially if it's well obfuscated or part of a new threat. However, they might detect and block it if it tries to do something suspicious when executed.

Since VirusTotal only used static scanning, its reports never were an accurate reflection of a malicious file's detection rate across antivirus products, even though many people interpreted them as such.

In reality, if a VirusTotal scan report shows no detection for a file it doesn't mean that it's clean and should be executed without worries. However, if a VirusTotal scan returns one or more positive results, especially from well-known antivirus products, then the file that triggered them should definitely not be be executed. So, there's still value in the system.

In an attempt to complement their static analysis reports with more information that could help users, security teams and researchers make better decisions about suspicious files, VirusTotal added behavioral information for Windows executables in 2012.

This information is extracted by running the file inside a controlled environment -- a sandbox -- and monitoring what actions it performs, like what files it creates, reads, or moves and what processes it spawns.

The same capability was added in 2013 for Android apps and, as of Tuesday, is also available for Mach-O executables, DMG files, or ZIP files containing Mac apps.

"Users may scan these file types directly on, with our OS X Uploader app, or via the API," VirusTotal team member Karl Hiramoto said in a blog post.

David Harley, a senior research fellow at antivirus vendor ESET and a vocal critic of using VirusTotal scans to make claims about the performance of antivirus products, feels that the addition of sandbox testing to the service is an improvement.

"This perhaps blurs the distinction slightly between VirusTotal’s service and other security services in a way that might cause further confusion among pseudo-testers," he said in a blog post. "But that’s not VT’s fault, and I think the value added to its services more than compensates."

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