That article was so horrendous, I'm going to attempt to rewrite it with more context:
Malware authors want to slip their malware into a victim's PC undetected, which means they need to know, ahead of time, whether it will be detected by antivirus tools. So they scan it with antivirus tools. However, there are so many such tools (and it's difficult to know which one a victim might have), it's time-efficient to centralize the scanning. This is done with a "multiscanner", which is a website that runs a bunch of antivirus tools to inspect any file that a user uploads. The results from the (dozens of) scanning tools are presented to the user in a webpage.
There are two kinds of multiscanners, however: Those run by/for the "good guys", where Jane Doe can go and upload a fishy file to see what the scan result looks like (as part of deciding whether she wants to run/install/trust it). These scanners send copies of uploaded files (at least, those which smell suspicious to a first-pass heuristic) to antivirus companies so they can be hand-evaluated, and folded into future detection signatures. If a malware author uploads their newest creation to check that it slips through undetected, chances are that a few hours later, that result will change!
Aaaaand, those run by/for the "bad guys", which work just the same way, except they don't send copies of the fishy files back to AV companies. This is most useful to malware authors who want to make sure their payloads are still stealthy, without tipping their hand to the AV companies. Just like the other multiscanners, this type presents the results to a user in a web page.
In either case, the link to the results page contains the checksum of the submitted file; it's just an easy way for such things to work.
The article's central point is that this latter class of multiscanner is very popular. Sometimes, malware authors will share a link to their results page as a way of asserting that their payload is undetected by any scanners. By skulking around the seedier parts of the internet, looking at malware advertisements, researchers collected a lot of these links, and then looked for the checksums on other multiscanner sites. Only about 25% of them showed up in a timely fashion.
[Ed. note: This can be improved by you, the reader, by uploading suspicious files to sites like Virustotal.]