My wife has got her Samsung Galaxy S6 infected with a virus

[AC Question]

it has hijacked the default internet browser

 

[kotsoum]

Perform a factory reset on your device from settings app and it will belong to the past! ;-)

 

[Rukbat]

If the virus installed as a system app, a factory reset won't touch it. Use an antivirus app and see if it detects it. If not, try Malwarebytes Anti-Malware. (Not all browser hijackers are viruses.)

 

[ToolWiz Privacy]

There might be two reasons:
1 you have installed and runned APPs from unidentified developers or sources.
2 If you have rooted your phone, some malware can get the superuser authority and infect your device.

To get rid of the virus, you can take the following steps:
1 use anti-virus application
2 reset your phone
3 install a new ROM