Web ads aren't just annoying, they can also be the source of a malware infection that attempts to steal your identity. In her September 15, 2009 InSecurity Complex blog, Elinor Mills describes how ads are being used by criminals to trick people into buying fake antivirus software, among other nefarious purposes.
Technology to block the ads that appear on Web pages has been around for almost as long as the ads themselves. No doubt someone will point out the irony of a blog that relies on ads for its livelihood explaining how to prevent them from appearing. For better or worse, few people will actually take the time to use an ad blocker when they browse. I don't think online advertisers are losing much sleep over the technology—yet.
Skip the ads when viewing pages in
One of the most popular Firefox add-ons is Adblock Plus, which puts an "ABP" icon on the far right of the main menu. Click it (or press Ctrl-Shift-V) to view the blockable items on the current page. Choose the down arrow next to the icon to open the program's Preferences dialog, disable ads on the page or site, or select other options.
Hovering over the Adblock Plus icon shows the add-on's status and the number of blocked and blockable items on the current page. You can also open the program's Preferences dialog by clicking Tools > Adblock Plus Preferences. There you can subscribe to an ad filter, import and export blocklists, view and reset your "hit" list, and change your view. Another option lets you remove the block tabs that appear by default on Flash and Java items.
Block ads in Internet Explorer
Back in January 2008, I called the free IE7Pro "(t)he only Internet Explorer 7 add-on you'll ever need." Well, the name's the same, but the program now works with IE 8 as well. Blocking ads in IE is as easy as downloading and installing IE7Pro, clicking Tools > IE7Pro Preferences, and checking Ad Blocker on the main Modules tab. The program blocks Flash, Java, pop-ups, pop-unders, and other types of Web ads.
To put a finer point on your IE ad blocking, select the AD Blocker option on the left side of the Preferences window. There you can enable the program's Flash blocker, which is off by default. You can also make changes to the IE7Pro filters, but you can't import or export filters as easily as you can using Firefox's Adblock Plus.
Use a proxy to squash ads in Chrome
It isn't surprising that Google decided not to include an ad blocker in its Chrome browser. After all, the company makes quite a bit of money from serving up those ads, so helping people to block them would be self-defeating. I found a couple of ad-blocking extensions for Chrome, but after taking a look at them, I just didn't trust them.
In one case, the home page of the extension's provider was crowded with ads itself. And another Chrome ad blocker I looked at had an unfinished appearance. The best solution I could find for blocking ads in Chrome is the Privoxy Web proxy, which is available on Source Forge. Configuring the add-on is a challenge, but a post on the GeekZone tech community boils it down nicely to seven steps.
Block ads in Opera, no add-ons required
The best way I found to block ads in the Opera browser is to use the program's built-in content blocker. To activate it, right-click anywhere on the page and choose Block Content. Only the blockable content on the page will be highlighted, and a toolbar appears at the top of the page. Choose an item to block it, and then click Done on the toolbar to reload the page minus the elements you selected.
To unblock an item, just reopen the Block Content toolbar and click the "Blocked Image" indicator. You can also view the URLs of all blocked items on a page, edit the entries, and add or delete items. There's no option to import or export a list of blocked URLs, however.
Bonus tip: Block ads and malicious sites via the free OpenDNS proxy service
Perhaps the greatest security resource on the Web is the free OpenDNS proxy service, which sends all your Internet traffic through a well-maintained set of filters to screen out ads as well as sites known to host malicious content. You can use the OpenDNS service to block gambling, adult, and other specific types of sites. For instructions on using OpenDNS, see Becky Waring's article "Use OpenDNS to surf safely with these tricks" on the Windows Secrets site.