Speaking of adds and how they get there.,
What you are seeing is an advertising technique called “remarketing.” It’s used by advertising networks, which are companies that websites contract with to present the advertisements you see. Most ads on Ask Leo!, for example, are provided by Google.1
It works like this:
You visit a shopping site, or a site that offers some kind of service. This site may or may not show ads, but they do include content from an advertising network.
The advertising network places a cookie on your computer. That cookie contains information to the effect of, “This computer was looking at X,” where X is the product or service offered by the site you’re visiting.
Eventually, you move on to another website — a site that also displays ads, and coincidentally uses the same advertising network as the site we started at.
That advertising network is given its own cookie back — the one that says, “This computer was looking at X” — and as a result, elects to show you ads for X.
It’s certainly not spyware, and it’s definitely not malicious software on your machine. It’s simply advertisers leveraging how the internet and web browsers work by showing you ads for things you’ve shown or someone in your home has shown an interest in.
There’s nothing you can really do about it without using an ad-blocking solution and clearing cookies