How does malware infect a computer?

You download a program that seems legit but is infact infected. Common ones are browser toolbars and animated mouse cursors. but free games, task bar applications, etc.
you need a virus blocker and firewall on windows computers. Whoever uses the computer needs to know that if the protection software says not to downlaod something, DO NOT turn off the software so you can download it.

There are security vulnerabilities that are coded into things like browsers especially things like JavaScript interpreters built into browsers. It’s really easy to make a security mistake when coding, and the playoffs can be monumental for discovering a 0 day exploit, so there are lots of people looking for these weaknesses, and given enough time they find them. Once found code can be written to exploit the vulnerability, and so it becomes easy for any malicious-minded person to write their own malicious app that profits from the exploit.

Other malware is installed because the user authorized it (because they just clicked “ok” instead of reading the pop-up window) not realizing what they were doing. Sometimes these are disguised as something the user wants like a “free copy of photoshop” that’s really just malware. This is known as a Trojan (like the horse—it looks good on the outside, you bring it into your gates and it’s not what it appears to be).

There is a lot more to this subject, I’ve just scratched the tip of the iceberg (to mix my metaphors).

Try typing this into your Chrome address bar: chrome://extensions

Delete anything that is there which you don’t recognize or trust. Chances are that a malicious web page installed a Chrome extension to create advertisements.

“Malware includes computer viruses, ransomware, worms, trojan horses, rootkits, keyloggers, dialers, spyware, adware, malicious browser helper objects and rogue security software.” (Wikipedia)

In my experience chrome is susceptible to a lot of virus attacks. Once I tried to download a game and it took a while to download. Next the game did not come up and instead I got a message saying that chrome crashed. I tried opening chrome again and again but it kept telling me that chrome has crashed. I switched to a different browser for a long while until one day I went back and tried to open it, and it worked. Sometimes I guess, the virus or whatever malware it was that made it crash, just disappears. FYI I even tried the extensions thing and it didn’t work.

The basic trick of malware installation is to copy a piece of code into a computer file and then manipulate the code on a program that runs on the computer, like the computer’s startup code or a browser, in such a way as to call the malware code. It is called a virus because it is analogous to the way that biological viruses work. A virus can’t reproduce on its own. It inserts its genetic code into a cells reproductive machinery so that the cell now reproduces viruses instead of new cells.

Malware comes in many forms (as noted in @mattbrowne‘s response, had I read that first), and sometimes one person’s malware is another’s preferred search engine or toolbar.

Forms of “malware” include viruses, trojan horse attacks and keyloggers which nearly any user would agree are “bad”, but extend through a gamut to include more or less innocuous programs that simply perform badly or inefficiently to those (such as the one you’ve apparently discovered) that try to sell you a product or service incessantly to those that add unwanted toolbars to your browser, hijack and change your home page and change your default search engine to one provided (most of the time “by request”, if you read the fine print on the EULA – End User License Agreement) of free or paid software that has been downloaded for use on the machine.

Sometimes malware comes hidden as something else: “Download this great calculator for free!” can be a garden-variety version of the Windows calculator with added software that unknowingly does something that the programmer wants and which you may not be at all aware of. Most often, I think, a lot of “free” software comes with an EULA that includes “opt-out” choices for browser home page changes, added “helpful” tool bars and search engine redirects that unwary users neglect to check off “No, I don’t want this.”

I had to read a lot of Chrome forums, but I found it and removed the adware. It was buried in the browser.

Malware always infects your PC via the means in the following: spam emails, scripts, sponsored links, downloaded files, free software programs and removable storage devices.