The reign of pointlessly destructive viruses has passed. Where viruses once ravaged your computer merely because the virus' authors wanted to demonstrate how 'clever' they were, viruses have been replaced by something more profitable: spyware, adware, and ransomware. As a method of distribution, malware-ridden ads (sometimes called 'Malvertising') spread far more easily than a conventional virus. The viruses of yesteryear required downloading and running that suspicious ".exe" file or opening that curious attachment in your inbox. Malvertising, on the other hand, requires nothing more than a browser and a website running ads from a compromised ad network.
When the ads aren't delivering malicious content to your PC, they're tracking you. They gather data on your browsing habits, which they send back to the advertisers in order to build a 'profile' about you. This profile will include whatever they can glean--what kind of computer (or phone/tablet/game console) you use, what sites you like to visit, and then any kind of demographic details that they might infer from those sites: your age, race, sex, religion, political leanings, sexual preferences, etc. The average website now reaches out to dozens of different ad networks as soon as the site is visited. This constant barrage of requests to third-party websites slows down your browsing experience, sucks up your bandwidth, and drains your battery.
When ads aren't tracking you, they're bugging you. As your page loads, noisy videos interrupt your reading and begin playing automatically. Intrusive, full-screen overlays obstruct the article you're trying to read, beg you to sign-up for their newsletter, and urge you to download their dedicated iPhone/Android 'app' in order to browse a single website; your only respite lies in the purposefully-obscured 'X' button in the bottom-right corner of the window, tastefully placed so as to be out-of-reach on most devices without scrolling. Should you miss the button, we hope you enjoy the sudden redirection to the affiliate's website, thereby displacing you from the page you actually wanted to read.
Ads are pervasive, invasive, and dangerous. While it has been argued that the influx of ads continue to power the "free and open" web, it comes at the cost of your privacy, your security, and your sanity. An Adblocker can stop these ads from displaying on the webpages and prevent the page from reaching out to third-party websites for the purposes of tracking. In doing so, an adblocker can bring some level of enjoyability back to your browsing experience.
Find an adblocker you like and install it. uBlock Origin is highly recommended if it supports your platform:
Adblock Plus is a popular alternative to uBlock Origin (UBO for short). ABP contains an optional whitelist of "acceptable" ads, which it will allow to slip past the adblocker, so that websites you visit can maintain their stream of revenue if they promise not to bother you with excessive or obnoxious ads. In theory, this allows the visitor to continue supporting sites they like while sending a message that the annoying ads need to stop. In practice, however, ABP derives considerable revenue from this certification process, which makes it feel more like a racket than a consumer protection service. To boot, Adblock Plus now sells ads, which seems like a conflict of interest for an adblocker. For this reason, UBO remains the recommendation.
For mobile phones, the landscape is a bit different. Google Chrome is available on iOS and Android, but Google does not allow extensions on Chrome mobile, so an adblocker is out. Firefox for Android still allows add-ons, and so uBlock Origin can still be installed. On iPhones, ad blocking is supported on Safari. Possible adblockers for iOS may be reviewed here. A direct recommendation is not provided due to lack of familiarity with Safari.
There are a couple of ways that the 'static' advertisements of the past different from today's targeted advertising:
Adblockers can function in a few ways. One is by using a set of rules/filters from a maintained database like EasyList, which documents domains that are known to be connected to ad networks. When the adblocker sees that a webpage is pulling resources from these domains, it will block the outgoing connection to those domains. Thus the domain does not send back the ad's resources, and the ad does not display. Other adblockers go a step further and stop any request that goes to a third-party domain, under the assumption that anything which is not delivered via the site itself is probably a malicious third party.
Yes, and there are legitimate reasons why it might do so. Many sites use third party content delivery networks (often called a "CDN") in order to handle the bulk of heavy lifting when it comes to serving particular pieces of content to users. Another legitimate use might be if a website relies on a third-party payment processor (such as Stripe, Amazon, Paypal, etc.) in order to securely process your credit card payment. Even as something as simple as displaying an image that is hosted on another website technically requires reaching out to a third-party domain in order to fetch that image.
Generally, no, it should not. But on the off-chance that it does, most adblockers can be turned off temporarily or white-listed for a particular page so as not to interfere with its functionality.
Most operating systems now have built-in anti-virus and firewall. The need for third-party AV and firewall solutions has diminished. On an operating system like ChromeOS (used in Chromebooks), the user is not even permitted to install programs, and so anti-virus would be redundant. Because the average user spends so much of their time in the browser, and because the internet itself is still such an insecure place, the most pressing recommendation I can give to anyone using a computer right now is to make sure that their browser has an adblocker. Ten years ago, if I were "setting up" a computer for a friend or relative, I would probably have installed a free anti-virus scanner and ZoneAlarm firewall. Today, I will install for them a non-Internet Explorer browser and an adblocker.
As previously mentioned, you can always white-list or disable your adblocker for the specific page in question. However, this does not encourage the site to stop using obnoxious or intrusive ads--it merely encourages the sites to guilt-trip you into accepting them. Some sites have ceased using ad networks and have returned to displaying individual ads from a hand-curated list of sponsors. This bypasses the adblocker, since the images are now being stored on the first party domain. However, it also mitigates the security concern, since the website owner personally vetted the ads being displayed on the page. It is a return to form from the days of magazine ads, and while perhaps it is less profitable, it is far less intrusive.
Other sites have begun offering paid, subscription-based logins where the site is naturally free of ads when logged in with a paid account. If you wish to go down that route, I would advise verifying first that the logins are truly "ad-free" and not simply "less intrusive." There is little reason to pay a website that still tracks you.