MOST KNOWN PC VIRUSES:

Not to be confused with adware, malvertising is the use of legitimate ads or ad networks to covertly deliver malware to unsuspecting users’ computers. For example, a cybercriminal might pay to place an ad on a legitimate website. When a user clicks on the ad, code in the ad either redirects them to a malicious website or installs malware on their computer. 

In some cases, the malware embedded in an ad might execute automatically without any action from the user, a technique referred to as a “drive-by download.”

 Worms have been around even longer than computer viruses, all the way back to mainframe days. Email brought them into fashion in the late 1990s, and for nearly a decade, computer security pros were besieged by malicious worms that arrived as message attachments. 

One person would open a wormed email and the entire company would be infected in short order. 

Malware programs that encrypt your data and hold it as hostage waiting for a cryptocurrency pay off has been a huge percentage of the malware for the last few years, and the percentage is still growing. 

Ransomware has often crippled companies, hospitals, police departments, and even entire cities.

If you're lucky, the only malware program you've come in contact with is adware, which attempts to expose the compromised end-user to unwanted, potentially malicious advertising. 

A common adware program might redirect a user's browser searches to look-alike web pages that contain other product promotions.

Spyware is most often used by people who want to check on the computer activities of loved ones. Of course, in targeted attacks, criminals can use spyware to log the keystrokes of victims and gain access to passwords or intellectual property.

Adware and spyware programs are usually the easiest to remove, often because they aren't nearly as nefarious in their intentions as other types of malware. Find the malicious executable and prevent it from being executed — you're done.

 If you're lucky, you can find malicious executables using a program like Microsoft's Autoruns, Microsoft’s Process Explorer, or Silent Runners. 

If the malware program is stealthy, you'll have to remove the hiding component from memory first (if possible), then work on extricating the rest of the program.

 Often, I'll boot Microsoft Windows into Safe Mode or through another method, remove the suspected stealth component (sometimes by just renaming it), and run a good antivirus scanner a few times to clean up the remainders after the stealth part is removed.