Google's update began at around January 5th and lasted for about 5 days. (According to some of the tracking tools). Some users also reported additional volatility later this month (up to the 20th). It is not known exactly what it was, but some of the Webmasterworld forum users, one of the oldest webmaster forums, reported an increase in traffic.
It seems that allot of sites that were affected by the “Medic” update suffered the same impact this time around: Car manufacturers sites, grooming and fitness sites, medical, education and labor sites and also government and law. Basically sites related to style and quality of life or high-cost products and services were affected the most.
Although the update was not officially approved by Google, the fact that it was released in the first quarter of the year suggests that it might be a “Core” update, just like older “Core” updates Google confirmed in retrospect.
What to do if your site was damaged?
Because the update is quite similar to the Medic update, it is important to continue paying attention to the three elements of the E-A-T (see the Medic update): Expertise, Authoritativeness, and Trustworthiness. Improve the clarity of your content, make it more accessible to the unprofessional information seekers, and add references from other sources, similar to Wikipedia.
Also, since quite a few of the affected sites are commercial, it is important to link to and from different business assets such as social media profile pages, reviews, etc.