Online users who have received unexpected email messages with attached files with names ending with ".7z" are asked not to open them. This is because the fake email messages are being sent by cyber criminals and the attachments are 7-Zip compressed archived files that contain malware, malicious programs or computer viruses. And, any attempt to open the malicious attachments will result in the recipients getting their computers infected with a virus, Trojan horse, spyware, ransomware or other malware.
A Sample of a Malicious 7-Zip Archive (.7z) Email Message
Subject: Emailed Invoice - 107681:1
Date: Wed 30/08/2017 22:04
From: Nickolas Leonard
Attachment: I_107681-1.7z (3 KB)
The 7-Zip compression is similar to ZIP which is the most popular file compression or archive formats.
Cyber criminals usually store their malware in compressed files to help prevent antivirus software from detecting them. In other words, they do it because the compressed malicious email attachments may bypass the recipients' antivirus software.
What is a 7-Zip file?
Files with the extension .7z are compressed archive files created with 7-Zip open source software. These files are created using a compression method called LZMA, which is an algorithm for lossless data compression—a type of compression known for reducing file size while preserving quality.