Malvertising, short for malicious advertising, is the use of online advertisements to deliver malware or lead people to scams. The harmful ad is placed through legitimate ad networks, so it can appear on reputable sites whose owners never wrote the bad code.
Why it matters
Ads are often loaded from third parties through automated auctions, and site owners do not review every ad that appears. A malicious advertiser can pass checks, then switch the ad's behavior later. Some attacks use redirects that send visitors to fake update or support pages, and in rarer cases exploit browser flaws. Keeping browsers and systems patched reduces the risk, and ad blockers can help avoid it.
Example
A visitor reads a news page. A banner ad loads a script that redirects the whole tab to a page claiming "Your browser is out of date, install this update". The page belongs to the attacker, and the file offered is malware. The news site itself was not hacked.
Common mistakes
- Assuming that a trusted website means every ad on it is safe.
- Installing a "browser update" or "player" offered by a pop-up. Updates should come from the browser's own settings.
- Skipping updates, which leaves known flaws available to exploit.
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