Nearly a million fixed-line network customers of German telecommunications company Deutsche Telekom AG on Sunday began experiencing service disruptions, possibly to due hacker sabotage, the company has announced.

The telecom connectivity issues appear to have affected approximately 900,000 customers using Speedport W 921V or Speedport W 723V Type B routers. On Monday, the company made available a corrective software update for these routers, which provide users with phone, Internet access and online TV reception.

Deutsche Telekom, which owns a majority of T-Mobile US, services roughly 20 million fixed-network customers. Those impacted by the outage have been experiencing “temporary problems or very marked fluctuations in quality,” the company explained in a statement, while others were getting no service at all. “Based on the error pattern, we cannot exclude the possibility that the routers have been targeted by external parties with the result that they can no longer register on the network,” the company concluded.

A Reuters report quoted several German government sources as saying that the incident “obviously looks like the work of hackers.”