I don't have a clue what "online" means - you must download 6 megabytes of software before it checks for viruses. There are also over 100 new registry values.
In 1998, I deleted my virus check software from my home system because it caused my new system to not boot. I have run unprotected ever since.
The last time I got hit with a virus was at work - just opening a web page infected my system. From that, I learned that the best way to protect yourself from these problems was to remove Microsoft email programs from your system (because they run scripts).
I recently saw that I could check the system for free, and presumably by not downloading any software (I figured that this was impossible, but worth trying). Since I download other software all the time, I decided to try this and see what happened.
Files downloaded to your system
The software was loaded in c:\WINDOWS\Downloaded Program Files - no, there was not an option to load it somewhere else. There were 5 *.dll files (programs), an *.vbx file (another program), numerous *.dat files (presumably virus definitions), and a few others, for a total of 35 files. Of course, in standard Microsoft form, only 2 "files" are shown using Windows Explorer. You must go to a command prompt (a DOS window) to see the rest.
Windows explorer only reports 600 KB,
but dir reports close to 6 megabytes!
(I no longer intentionally load any software
In addition, there were numerous registry modifications - 108 keys and 121 values.
How do I know this, I ran InCtrl before starting the scan. (I no longer provide links to this because it is no longer free.)
UUD.COM is infected with Kaos4 MUUD.COM is infected with Kaos4When I originally downloaded these, the download page warned about false positives. I have used the software and no additional files are infected.
This is one of the reasons that I have such a high opinion of anti-virus software.
(There's nothing wrong with MS Word ... as long as you never open a file written on another system. Same for the other office programs - as long as you create content, there is no problem. You have to open a file from someone else to get infected.)