Correction appended Friday, Oct. 21

Internet users are reporting widespread issues Friday morning, particularly along the eastern seaboard, as several websites and services aren’t loading normally.

The problem seems be due to a Distributed Denial of Service (DDoS) attack against Dyn, which provides Domain Name Service infrastructure to a variety of major Internet brands. DDoS attacks involve sending a flood of bogus Internet traffic toward a target in hopes of overloading it and knocking it offline. DNS acts as a kind of phone book for the Internet, helping your Internet browser take “www.time.com,” for instance, and retrieve TIME’s website.

This attack isn’t knocking your favorite websites offline, per se. It’s just making them harder for your browser to find. Still, it highlights how vulnerable the Internet can be to this sort of digital assault. It’s unclear at this time who’s behind the activity.

Read more: You asked: How does the Internet work?

“Starting at 11:10 UTC on October 21th-Friday 2016 we began monitoring and mitigating a DDoS attack against our Dyn Managed DNS infrastructure,” reads a status update from Dyn posted early Friday. “Some customers may experience increased DNS query latency and delayed zone propagation during this time. Updates will be posted as information becomes available.”

Update: According to Dyn, “services have been restored to normal as of 13:20 UTC.”

Update 2: Dyn said Friday afternoon that the DDoS attacks are ongoing. Meanwhile, Reuters is reporting that U.S. government officials are investigating whether the incident is a “criminal act.”

Update 3: Dyn said later Friday that it’s experiencing a third wave of DDoS attacks. The origin of the attacks remains unclear.

Friday’s problems come just about a month after security researchers recorded what’s believed to be the largest DDoS attack in history.

Here’s a map from Downdetector highlighting the geographic extent of the issue:

Level3 DDoS Map Level3

Correction: The original version of this article misstated the source of the map above. It is from Downdetector.

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Write to Alex Fitzpatrick at alex.fitzpatrick@time.com.