If you run a website which is open to user comments, you may have to contend with comment spam at some point. It can be extremely annoying, but there are fortunately several techniques which can be used to fight it. Ideally, you can reach a solution which filters out most of your comment spam without inconveniencing readers. You may want to think about integrating several techniques to stop spammers from several angles.
Before plunging into ways to fight comment spam, it can help to know what it is. Essentially, it is an unwanted comment which is used to advertise a product or website; such comments are usually posted by a bot, rather than a real human being, and they can pile up alarmingly quickly. Some spammers also use trackback spam to advance themselves, since trackbacks can be used to disseminate links to their sites.
The first step you can take is using a spam filter. Many blogging platforms have spam filters which are built in, and you can adjust the aggressiveness of the filter or create a list of keywords for moderation. Comment spam often includes gibberish, reference to prescription drugs, and other obvious keywords which normal commenters do not use. You set set up a spam filter which automatically deletes messages, or holds questionable messages for you to approve before posting.
You can also utilize IP banning software. Several companies have created so-called “blacklists” of IPs which are routinely used for spam, and you can block these people from accessing your site or leaving comments. Many website administration tools allow you to manually block specific IP addresses; you can also use this tool for trolls and other obnoxious commenters.
Both of these measures are designed to fight comment spam without inconveniencing your readers. If comment spam continues to be a problem, you can jump to more assertive measures. Some site owners, for example, put all comments into moderation, meaning that every comment must be manually approved before it can be posted. While this forces legitimate comments to be held until you have a chance to look at your comments, it also allows you to head off disastrous comment threads before they get serious, which can be an advantage. You can also close comments and trackbacks on old posts, giving spammers less fodder to work with.
If you find that these measures were not effective, you may have to turn to techniques which require your users to jump through a few hoops. One technique is registration; you can require all users to register before they post comments, which can reduce the amount of spam which filters through. You can also use a CAPTCHA, a tool which issues a challenge to each commenter. For example, a CAPTCHA might be a hidden word inside an image; a real person can find the word and type it into a confirmation box, while a spamming bot cannot. However, CAPTCHAs pose a serious obstacle to users with disabilities, and if you choose to use a CAPTCHA, you should consider installing a workaround for impaired users.
If you do turn to tools like registration and CAPTCHAs, you will unfortunately lose some commenters. Some people are uncomfortable with registration, while other people are not inclined to comment if they have to put effort into the process. These tools are also not a guaranteed insurance against comment spam, so you should weigh the costs and benefits carefully.
New measures to combat comment spam are always emerging; if you use a specific type of software to manage your website, keep up with the developer's notes and software updates. In addition to keying you in to new features, notes and updates will also keep your version of the software current, ensuring that malicious people and software cannot target the security holes which are inevitably found eventually in every software release.