The FBI recently made a formal PSA about a piece of malware called VPNFilter that is infecting routers used in homes and small businesses at an alarming rate. The difference in this strain versus others is that no one is quite sure what the impact will be, since it is a very sophisticated piece of malicious software.
What VPNFilter malware does
The malware uses default credentials to infect routers, meaning that it can be avoided by changing passwords and other security on devices. It "sniffs" network data where an infected device is physically located, gathering the passwords, usernames, and other credentials on that network. This can include supervisory control and data. And VPNFilter malware can serve as a relay point to hide the origin of incoming attacks that later use that information.
This software installs itself in three stages, and the impact of the third stage is not well known. The FBI has advised that everyone should reboot their routers, under the belief that this will mitigate the malware and prevent the third stage from executing in the future. However, this is not entirely correct in a technical sense.