What indicates that an attack is not being eradicated by anti-malware programs?

A zero-day attack refers to an exploitation of a vulnerability in software that is unknown to the vendor and for which no patch or defense has been developed. This type of attack is particularly dangerous because it occurs before the developers can respond with a remedy. As such, traditional anti-malware programs might not recognize the threat because they rely on known signatures or behavioral patterns. When a zero-day vulnerability is exploited, it can lead to persistent threats within a network that anti-malware solutions may fail to eradicate, especially if those solutions aren't designed to deal with unknown vulnerabilities.

In contrast, phishing attacks are generally recognized by anti-malware tools, as they often rely on established patterns of malicious behavior that can be flagged. Denial of Service attacks focus on overwhelming services rather than directly infecting systems, and while they can be disruptive, they don't necessarily indicate that malware is present or not being removed. Keylogging, which captures keystrokes to steal information, can be identified and addressed by many security solutions, thus not serving as a strong indicator of failure in malware eradication processes.