Russian state hackers are engaged in a large-scale global cyber campaign to gain access to Signal and WhatsApp accounts belonging to dignitaries, military personnel and civil servants. The Dutch intelligence and security services MIVD and AIVD can confirm that targets and victims of the campaign include Dutch government employees. The Dutch services also believe that other persons of interest to the Russian government, such as journalists, may possibly be targeted by this campaign.
I just had a quick look, it appears to be mostly a targeted attack based on social engineering.
A good reason to only use usernames.