Basecamp, maker of the popular project-management app by the same name, was back online Monday afternoon after sustaining a crippling denial-of-service attack earlier in the day that rendered its services unavailable to virtually all users.

In a blog post published Monday, Basecamp officials said the attack began after they spurned a demand to pay an unspecified ransom to avoid a threatened assault on their site. The flood of data that came after the demand was rebuffed peaked at about 20 gigabits per second, preventing legitimate traffic from passing through the site’s overwhelmed data connections.

“We’ve learned that the very same criminals currently attacking and trying to extort us hit others just last week,” the Basecamp blog post stated. “We’re comparing notes with everyone affected who have been in touch. The blackmail came from an address matching this pattern: dari***@gmail.com. If you have been extorted by this person, please get in contact so we can compare notes on both technical defenses and the law enforcement effort to hunt them down.”