On Saturday, Rogers Communications said it had restored service for the “vast majority” of customers affected by the outage that left many Canadians without access to the internet. “As our services come back online and traffic volumes return to normal, some customers may experience a delay in regaining full service," the telecom said in a Twitter update posted late Thursday evening. It later promised it was “working hard” to get any customers still without internet access back online “as quickly as possible.”

In a letter attributed to president and CEO Tony Staffieri, Rogers said it was “working to fully understand the root cause of this outage,” and that it would make all “the changes necessary” to avoid a repeat in the future. Additionally, the company promised to send a bill credit to every customer affected by the outage.

While Rogers has yet to share what caused its entire network to go down for the better part of an entire day, DDoS mitigation company Cloudflare provided a possible answer. “Based on what we’re seeing and similar incidents in the past, we believe this is likely to be an internal error, not a cyber attack,” the company said in a blog post published on Friday. Cloudflare speculated that a Border Gateway Protocol (BGP) issue likely contributed to the outage. A “routine BGP update gone wrong” was the cause of the massive outage that took down Facebook, Instagram and WhatsApp last fall.

Whatever led to the outage, its effect was easy to see. People crowded into cafes and public libraries so that they could use their phones and computers. At one point, Toronto Police even noted some people couldn’t call 911 due to the outage. Across the country, Interac, the system Canadian banks use to connect their networks, was down, leading to debit cards and ATMs not working. One analysis by internet monitoring organization NetBlocks showed that Canada’s national connectivity dropped to 75 percent of normal levels during the event. If nothing else, the episode is likely to reignite conversation within Canada about the dominance Rogers has over the national telecom market.