Malicious code is code that exploits vulnerabilities to spread malicious payloads to computer systems.
Most viruses and trojans depend on humans to spread them
Computer worms spread by themselves.
This exploits a Zero-day vulnerability, which is a vulnerability that has existed since the release of the software or product, that have not been addressed by cybersecurity.
Is the time between the release of the software and the first fix, that solves the bug.
Anyone with minimal level of technical expertise can download a virus (ready-to-use software) and unleash it in the internet.
These criminals are often located in countries with weak law enforcement.
Is when you unintentionally download something, without explicitly clicking on a download link.
It could happen when visiting a website or clicking a pop-up window. It takes advantage of security flaws of your operating system or app.
The Zeus Trojan (ZeuS, Zbot, Trojan ZeuS)
→ It was often used to steal banking information using man-in-the-browser keystroke logging and form grabbing.
Are often created by military units, intelligence agencies or shadowy groups that are most likely associated with government agencies.