Most authors of website malware usually rely on the same tricks, making it easy for malware researchers to spot obfuscated code, random files that don’t belong, and malicious lines injected at the top of a file. However, it can become difficult when the malware is buried deep within the lines of code on normal files.
Why is some malware harder to spot than others?
An attacker’s primary goal is to retain access to an infected site, so they go to great lengths to hide their access methods. There may be hundreds of malicious files that are easy to find. As long as the attacker can regain access, ultimately reinfecting your website, it doesn’t really matter how clever they are in hiding the payload. It’s why it is so important to place extra emphasis in identifying the access vector, most often known as a backdoor.