I wonder if trojan activity could possibly consume extra hard disk space. When running my favorite registry cleaner (PCtuner by Quickheal, an antivirus company in India), I would pick up at least 600 invalid registry entries in a 3 month period before I switched to Avast AV. Now it's closer to 100. However massive amounts of invalid registry entries point to the leftovers of spyware activity.
I worked in Internet tech support for Comcast and in my experience of talking to around 600 computer users per month: I think that most people have trojans sitting on their computer regardless of how great they think their antivirus program is. Most AV programs grew up in an age where viruses where just about anarchy. Now they are about business, as in grabbing your banking info to drain your account. Unfortunately a lot of the big names make more money when you call them for support ($85 to $300) than they get from selling their software. So why should they make a serious effort to protect you?
Information moves over the web in hops. When you are infected with a trojan, your computer becomes part of a network forwarding keystroke logging from other infected systems. When I was infected: Kaspersky informed me that I had 42 connections open to the internet (it finally let me know after I gave up on finding anything wrong and was removing it from my computer: I switched to Avast and the problem disappeared after running its famous boot scan).
This type of unauthorized activity keeps your hard drive spinning when you aren't actually doing anything on your computer. Ultimately your drive will burn up prematurely. Your Internet experience will be slower than it should be and you will often experience inexplicable delays when trying to connect to a page or an object.
Internet providers have simply given up and keep throwing more and more speed at their customers. It only takes two connections to download most web pages. Customers blame the cable company because the speed problems evaporate when they move their computer to a different network, such as a public wifi spot, their office or a vacation home. However it's only because the trojan network can't find you at the new location.
You can get these buggers on any legitimate website. Kid's game sites and Facebook aps are the worst: nothing is really free. The website owner doesn't typically control which banners are shown. They come from a third-party banner network. The active X controls which help advertisers see where you are surfing, in order to serve up targeted ads also let anyone with a credit card to take out an ad and spy on you. Overseas, American identity theft is big business and they have plenty of stolen credit card numbers with which to take out illegitimate banner ads.
One lady who called in had $1000 yanked out of her banking account after buying a phone online. Another gentleman found charges for airline tickets from overseas on his bank statement.
I wonder if this kind of unauthorized activity consumes hard disk space as well.
Once your browser has been thrashed with bad active X controls, you have to go in and download a fresh copy after cleaning up the malware. Its always a good idea to have at least two browsers on your computer, in case Internet Explorer goes defunct you can always go in via Google Chrome and download a new copy. Even if you never use IE for surfing, you have to reinstall it after any kind of infection.
Contrary to popular belief, Macs, Smartphones and even Linux all run Microsoft Active X to surf the web. All of these devices get viruses and need protection.
Whenever I get a new computer I go in and remove all the factory programs using freeware called "Revo Uninstaller". If you simply use the Windows uninstaller, many programs leave behind hundreds if not thousands of files on your computer, which may end up causing you problems. So called "program updaters" are designed to spy on whether you are stealing the trial programs that came with your computer. Unfortunately this also opens a back door to other intruders.
The way they get even with you for removing one antivirus program is by telling you to reboot right away. This causes your system to come up totally unprotected and nasty things that weren't caught take over. The whole thing often dies within an hour. I've seen it over and over when people switch to from Internet provider to another. They have to remove from one "free" included AV program and install a new one and suddenly their computer becomes useless. You want to tell the computer that you will "reboot later" and then install a new Antivirus program BEFORE rebooting.
My step son has ruined both his mom's and dad's computer. If you have a kid who likes to play online games, take a few moments to research the process of restoring your computer to factory settings from the boot menu. Have an understanding with your kid: that if the computer freezes up during a game they should NOT try to turn it back on. You might get only one chance to even make it to the boot up menu. More damage is done when you bring the system up the second time and then all you get is NOTHING upon turning it on. Might not be a bad idea these days to have a $100 pawnshop computer for the kids. Try to stick with Windows Vista or later as they all have built-in factory recovery programs. Check to see that the factory recovery partition has not been removed.
I stick with the free version of Avast as I think the paid version has become over bloated and interferes with what you are doing: the free version is very lite and transparent. I wish more AV programs would do something about pop-up virus attacks and viruses that hop onto your computer from other computers at wifi spots. I haven't found ANY programs to defend against these issues so far. So I keep a backup snap shot of my personal optimized setup on my Acer Vista laptop. Whenever my computer does strange things: I simply restore it to that perfect point. (Note: this is different than the built-in system restore that comes with Windows.)
Of course you can lose everything when you do a full system restore: however I keep all my own data on a separate hard disk partition. I also back up critical files to my USB drive.
I realize this seems to be a little off topic: but I think the quantities of used disk space
Carol is talking about are much larger than can be accounted for with the other explanations offered.
