We often see publishers in the AdSense Help Forum asking us to help them because their accounts were disabled. For many, the policy violations on their sites preclude us from being of much assistance. You must follow the AdSense Program Policies and the Webmaster Guidelines. If you don't, there's a good chance your account will be disabled.
Other publishers have had accounts disabled for reasons such as "invalid activity" and many ask us how this can be when they haven't clicked their own ads.
You don't have to click one (or more) ads on your website to have invalid or suspicious activity. OTHER people can cause this, and while it isn't your fault they've done so, it is your responsibility as a publisher to do everything you can to protect both the advertiser (who is the one paying the bills) and your account.
So...I can see the wheels spinning already. The big question is "well how do we do that?".
Adsense itself provides very little in the way of options that offer any sort of "protection". They offer no blocking mechanism to stop people from visiting your site or clicking your ads (notice I have no ads on this blog? Can you figure out why?)
But because they don't hand you a method to do that doesn't mean there aren't ways to look out for problem areas in your account and on your websites.
The first step: do not place adsense ads on your website and then forget about monitoring them. We've seen many publishers who placed ads on their site(s) and then didn't bother checking their sites after that. Once in a while they'd check their AdSense accounts to see if they earned any money, but never really kept track of what was actually happening on their websites.
The second step: track, track and track. What that means is that you should find a third-party (ie: not one provided by adsense) statistical tracking code and install it on your website(s). Third party trackers often provide useful information that AdSense and Analytics doesn't - for instance, the IP address of all visitors and what those visitors looked at (what pages) while on your site, and what they clicked on . And this is information you need to help protect your account.
Warning: there is a word of warning that goes along with using third-party stats. These third-party scripts CANNOT, CANNOT, CANNOT (I'll repeat that just in case you didn't get it, CANNOT) tell the difference between a valid click for adsense and an invalid click. In a lot of cases, third-party stats register clicks that don't actually occur. I won't get into the hows and whys because that's a technical issue that would take way too long for me to explain, so you'll have to trust me a little on this. DO NOT expect these stats to show you the correct ad clicks for AdSense. What AdSense records as a click and what third-party trackers record as a click WILL NOT likely match. If that is going to freak you out some, then don't use third-party trackers. Unfortunately, this is likely going to be the only way to protect yourself. If you can ignore the differences in click records (just don't look at them in a third-party counter) then get one onto your site.
The third step: visit your third party stats and your adsense stats DAILY, or at the very least every other day. If you only look at them once a month it would be too late to head off any problems, or to institute control over any website that has become the target of some malicious "click-bomber".
HOW THE STATISTICS CAN HELP YOU
In the help forums we have a long-time publisher (known only as Publisher1) who has suffered through a very long bout of malicious behaviour from one visitor. His problem was spread out over many weeks and involved many, many fraudulent and invalid clicks, among other things.
Publisher1 still has his AdSense account though. And he was able to oust the click-bomber by taking a pro-active stance and by taking charge of the situation. How did he do that? I'll let him tell you the story, because he very kindly posted two articles to the AdSense Help forum that explain HOW to protect yourself against stuff like this. You may not be able to stop it from happening, but the steps you take when it does are what will help you keep your Adsense account.
FACING AND BEATING A CLICK-BOMBER'S ATTACK
The Crash Course Emergency Strategy for Click-bombing Attacks
Please, please, please go and read the information provided at those two links, and then bookmark them. You'll be doing yourself a big favour. Some day, you may need this information to keep your AdSense account alive.
Oh - one more thing. Remember to thank Publisher1 for sharing his experience to help others.