Hundreds of thousands of Deutsche Telekom customers in Germany have been hit by network outages that could be the work of hackers.

Deutsche Telekom said as many as 900,000, or about 4.5 percent of its 20 million fixed-line customers, began to have problems connecting to its network on Sunday afternoon.

The outages affected certain customer routers which are used to dial into the network and offer phone, Internet access and online TV reception, the company said.

Currently a software update is provided to all affected customers to fix the router problem. The software rollout already started and Deutsche Telekom said it "can see the success of this measure." The company's customers should unplug their router for 30 seconds. Afterwards when reactivating the router the new software will be installed automatically from the servers. Alternatively, the software update is available for download here www.telekom.de/stoerung and can be entered manually. In this case unplugging the router is still required.

"Based on the pattern of errors, it can not be ruled out that the router has been targeted externally, with the result that it can no longer log on to the network," Deutsche Telekom said in a statement on it website.