Step 1. Rule out malware
No ad blocker can block ads caused by malware. The only way to remove the ads is to remove the malware. Since no amount of troubleshooting will help if your computer is infected, the first step is to make sure the ads aren't malware. If you've already done this, continue to Step 2.
Step 2. Try some easy fixes
Check the AdBlock button in the browser toolbar. Is it gray, green, or showing a "thumbs-up"? Make sure AdBlock isn't paused and the site isn't whitelisted.
Try turning off the Acceptable Ads setting.
Click the AdBlock button in the browser toolbar and select Options. On the GENERAL tab, clear the check box next to Allow some non-intrusive advertising. Learn more about the Acceptable Ads program.
Try uninstalling and reinstalling AdBlock if you haven't already. (Be sure to copy any custom filters to a text file for safekeeping first. You'll need to add them again afterward. And by the way, if you don't want to donate to support AdBlock at this time, just close the payment page.)
If you have more than one ad blocker, including Ghostery, disable all of them except for AdBlock. Reload the page where you were seeing ads. (You shouldn't use more than one ad blocker at a time.).
Scan your computer for malware, even if you did Step 1 and you don't think the ads are malware.
We recommend Malwarebytes Anti-Malware Free for Windows or Mac. We're not affiliated with Malwarebytes; we've just found that their software tends to find malware that others miss.
Note: Ad blockers are not antivirus or anti-malware applications. If a malware-laden ad gets through, your computer can be infected. Always, always, always use protection on the Internet. If you don't have one, enter "best free antivirus mac," "best free antivirus windows," "best free anti-malware mac," or "best free anti-malware windows" in your favorite search engine.
Check to see whether you're in incognito or private mode. Some browsers (such as Chrome) don't allow extensions to work in an incognito or private browsing window until you enable them to do so.
Are the ads on a page you open by clicking a link on a different site, such as a news article on Facebook?
Step 3. Check for known issues with specific websites
Step 4. Check for issues with your browser
Test the site using a portable version of your browser
This step checks to see whether your browser or browser profile has been corrupted. If your browser or user profile isn't working properly, AdBlock won't, either.
You could uninstall and reinstall your browser, but that's inconvenient. Try it as a last resort. For now, install a portable version of your browser. The portable version will run alongside your existing browser, not replace it.
Install AdBlock in the portable browser and apply the same settings, filter list subscriptions, and custom filters (if any) as in your existing browser. Then visit a page where you were seeing ads.
If the ads are gone, then your existing browser or browser profile is the problem. Go ahead and reinstall your browser. We have instructions in the Browser Issues section of our Knowledge Base.
If the ads aren't gone, then try the troubleshooting steps in the sections below.
A bug in Microsoft Edge may be disabling AdBlock every time Windows is updated. Make sure AdBlock is turned on in Microsoft Edge's extension settings.
If you disabled the "non-intrusive advertising" setting in AdBlock's options, check to see whether it's been turned on again.
Nothing worked! Now what?
If the suggestions above haven't helped, then the ad simply slipped through the filter lists. We do not maintain the filter lists. That means that we can't fix a filter list that isn't blocking an ad. The best thing to do is to report the ad to the list authors so that they can update their filter list and block it for everyone.
If you'd rather not go to the trouble of reporting the ad, you can try to block it manually.
If the ad can't be blocked manually, try the suggestions under "Employ userscripts to thwart anti-adblocking sites" in this article.
What if everything we suggest fails? Unlike some other ad blockers, we don't take a "scorched earth" approach to ad blocking. You may see an ad because it just isn't possible for us to block it without breaking the site. Fortunately, this doesn't happen often!