Q. I clicked the link on your site to download Spybot-Search & Destroy. Spybot’s site said it accepts voluntary donations. When I tried to download the program, I was redirected to another site. I clicked the download link and ended up at a site called SpywareBot. The site’s free scan found spyware on my computer. You must pay for SpywareBot in order to remove the spyware! Is this a bait-and-switch scheme? Or was Spybot’s site hijacked?

A. I get questions similar to this one all the time. Someone visits a site I recommend and downloads something bad. Or a free program I recommended suddenly costs $30. They think the site I recommended is up to dirty tricks.

But the source of the problem is always the same: Google ads.

Let’s start at the very beginning. Spybot Search and Destroy is a free program. The developer includes a link on his site so users can make donations.

This is fair. You don’t have to make a donation. But the donations allow him to continue to develop the free program.

Now, the program can be downloaded directly from his site. There are also mirror sites where it can be downloaded. Regardless, it is free.

Some developers offer downloads via mirror sites to preserve bandwidth. Bandwidth is essentially data traffic. When you visit a site, data is exchanged between your computer and the site. Site owners must pay for the data transfer.

Downloading programs or other types of files quickly eats up a site’s bandwidth.

Sites often use advertising to subsidize the cost of bandwidth. The most ubiquitous online advertisements are Google’s small contextual ads. Google chooses the ad to display based on a page’s content. When someone clicks on an ad, the site owner gets a cut of advertising revenue.

Site owners have quite a bit of control over the ads. They choose where to place the ads on the site. They can also choose the ads’ color scheme.

The amount of text shown can also be customized. An ad can have several lines of text. Or, the ad can just be a few words. Close to the ads, you’ll see “Ads by Google.” This may be the only indication that links are actually ads.

Obviously, site owners want you to click the ads. Oftentimes, the ads are customized to look like any other link on the page. They may be placed where you’d expect to find navigational links.

Unfortunately, not everything advertised through Google is on the up and up. In fact, the ads can often lead you to shady software. That’s what’s going on here.

You visited Spybot’s site and were directed to a mirror site to download the program. At the mirror site, you mistakenly clicked an ad instead of the download link. You ended up at SpywareBot’s site.

There are many complaints online about SpywareBot. Apparently, it is rogue anti-spyware. It tricks you into purchasing the software with a free scan. SpywareBot claims that your machine is infected. But its software will fix the problem—for a charge!

To make matters worse, SpywareBot tries to masquerade as Spybot. Internet forums are littered with complaints from people who downloaded SpywareBot. They thought they were downloading Spybot.

I hope you didn’t give them any money. If the software is on your machine, you should run real anti-spyware software to remove it. Lavasoft's Ad-Aware and Microsoft Windows Defender are two free programs.

Of course, there’s also Spybot. Given your situation, I can understand if you’re hesitant to try downloading it again.

The moral of this story: Watch where you click! I have a theory about the Internet. Whatever site you’re visiting, porn, malware and other Web nasties are about five clicks away! It’s easy to end up in a bad place if you’re not careful.

I am very careful about sites and programs I recommend. I make sure the programs won’t harm your computer. I check sites for links to objectionable content. But Google ads are wildcards.