It's a known fact and we also can't deny the fact that the Darkweb in general give a boost for Bitcoin price . (Silk road for example)

It's interesting to see how there are other alternatives right now that have better technology for anonymity, but still Bitcoin is the #1 used coin. This speaks of how important network effect is and how hard other coins will have it to even pretend to take Bitcoins #1 spot.
And we soon will have tech that makes Bitcoin as anonymous as the "anonymous coins."

because of bitcoin's anonymity, it's really good to use on dark web. I'm not surprised to know this, but I have some concerns about the legality and price of bitcoin. well, will this issue make bitcoin be banned or kind of thing?

the case is a bit more serious as it has to do with hackers using bitcoin ransomware to lock out local government employees from their own computers.

As has been reported, city officials worked to get back up an running, but there were at least a few computers that had already been impacted by the ransomware. The result? Having those government computers hacked in return for roughly $730 in bitcoin. But unlike some cases (like the hospital that forked over the bitcoin before consulting law enforcement), in this instance, the city called upon law enforcement for help — scaring off the hackers.

The nuts and bolts of the the hospital story began last month in Los Angeles with $17,000 worth of bitcoin being paid out to hackers who took down a computer system — which, of course, included vital medical records. This is the type of malware that’s been most commonly showing up in headlines and has been on the rise across the U.S.