Threat actors are increasingly using a Delphi packer to shield their binaries from malware classification by antivirus software and other security solutions.

FireEye analyzed several samples carrying the “BobSoft Mini Delphi” signature and determined that the samples were consistent with Delphi code constructs. These findings revealed that the malware binaries had been packed using a Delphi packer.

The enterprise security firm observed the packed samples being dropped in various spam campaigns. One operation used an attached document with malicious macros to download the malware. Another leveraged a document that exploited an equation editor vulnerability to deploy its packed payload.

In its analysis, FireEye came across at least eight malware families using the Delphi packer for their campaigns. Lokibot was by far the most prominent, followed by the Pony downloader and NanoCore. Researchers also spotted a cryptomining threat called CoinMiner using the packer.

How Do Malicious Actors Avoid Malware Classification?

The Delphi packer is just the latest cybercriminal effort to prevent malware from being detected or reverse engineered. Attackers do this by concealing their payloads with code that’s not strictly malicious. In particular, packers use a technique called executable compression to make their files smaller. The Delphi packer adds on to this functionality by monitoring windows and mouse cursor movement for signs of a sandbox environment, in which case it puts itself into an infinite sleep.

Packers aren’t the only services that bad actors use to hide their malware. Malwarebytes noted that cybercriminals also turn to crypters, which use obfuscation or actual encryption to make their payloads undetectable, and protectors, which block reverse engineering attempts.

How to Protect Against Packed Malware

According to FireEye, security professionals can protect their organizations against packed malware by using sandbox environments that model real user behavior. The threat advisory on IBM X-Force Echange advises users to update their antivirus software and verify the legitimacy of any unsolicited email attachment. Finally, security personnel should analyze threat intelligence to learn about the latest packers that are available in dark web marketplaces.

Sources: FireEye, Malwarebytes