Users who don't want to be infected can mitigate the risk -- the simplest way of doing this is by using a on the router or modem. Users can also address the problem by keeping their firmware up-to-date and by disabling remote-access services.

In recent years, hackers have started looking at devices such as routers, which are often not properly secured, Vykopal said. "They are not regularly patched and updated, even though the patches are available." The devices "are also continuously connected to the Internet and they are up for days and months," he said.

In the future, he expects that even more malware will target these devices.

Despite their rarity, router-based botnets are not particularly hard to create, said Dancho Danchev, an independent cyber threats analyst, speaking via instant message. "Router-based botnets are not rocket science given a common flaw can be exploited, and every then and now [one] appears."