Adware

Picture someone handing you a free pack of tissues on the street. You open it, and a pile of ad flyers spills out. Adware gets onto your computer and phone in a similar way. When you install a handy free tool or a simple game, it slips in quietly alongside it, without you noticing.

Once it's installed, ad pop-ups keep appearing in every corner of your browser. Even if you close every browser window, an ad can suddenly jump up in the middle of your desktop and interrupt whatever you're doing.

Blasting out ads like this to get you to click and to collect ad revenue is the main goal of adware. It forces you to look at screens you never asked for, which is a real hassle.

It may also watch which words you search for and then show ads for related products. Sneaking in by trickery and chasing profit is adware's signature move.

Not every program that shows ads is automatically labeled malware. Plenty of phone apps are free because they politely show a banner ad at the bottom of the screen. In a broad sense, those count as ad-supported software too.

But the story changes completely if a program installs itself without your clear consent, or if it won't go away no matter how hard you try to remove it in the Control Panel. If it locks your browser's home page onto some random shopping site, or secretly peeks at your browsing history, security software will classify it as a potentially unwanted program (PUP) or as malicious software, and block it. Where exactly the line falls differs a bit from one security company to another.

If adware keeps downloading ad data in the background (the hidden behind-the-scenes layer), it also puts a heavy load on your device. It needlessly hogs the processor and memory, which are your computer's brain.

The result can be a noticeably slower internet connection and a battery that drains fast on your laptop or phone.

On a PC, adware mostly comes along when you download free programs from websites you can't trace back to a trustworthy source. On a phone, it sometimes hides inside a game or utility app on the official app store and only gets spotted later. If you carelessly click "Express install" or "Recommended install" when setting up free software, adware often gets installed as part of the bundle.

So always choose "Custom install" during setup. Then carefully uncheck the hidden boxes for add-on partner programs, and you can stop ad programs before they get in.

If adware has already got you and your screen is covered in ads, the regular uninstall feature often won't fix everything. That's because adware tucks leftover files deep inside the system.

In that case, run a trusted, dedicated anti-malware tool and do a thorough scan. Your device only gets back its original snappy speed once the hidden leftover files and registry entries (settings data) are cleaned out too.