  Abridged: The interest towards searches for extraterrestrial civilizations
(ETCs) was boosted by the discovery of thousands of exoplanets. We turn to the
classification of ETCs for new considerations that may help to design better
strategies for ETCs searches. We take a basic taxonomic approach to ETCs and
investigate the implications of the new classification on ETCs observational
patterns. We use as a counter-example to our qualitative classification the
quantitative scheme of Kardashev. We propose a classification based on the
abilities of ETCs to modify their environment and to integrate with it: Class 0
uses the environment as it is, Class 1 modifies the it to fit its needs, Class
2 modifies itself to fit the environment and Class 3 ETC is fully integrated
with the environment. Combined with the classical Kardashev's scale our scheme
forms a 2d scheme for interpreting ETC properties. The new framework makes it
obvious that the available energy is not an unique measure of ETCs, it may not
even correlate with how well that energy is used. The possibility for progress
without increased energy consumption implies lower detectability, so the
existence of a Kardashev Type III ETC in the Milky Way cannot be ruled out.
This reasoning weakens the Fermi paradox, allowing the existence of advanced,
yet not energy hungry, low detectability ETCs. The integration of ETCs with
environment makes it impossible to tell apart technosignatures from natural
phenomena. Thus, the most likely opportunity for SETI searches is to look for
beacons, specifically set up by them for young civilizations like us (if they
want to do that is a matter of speculation). The other SETI window is to search
for ETCs at technological level close to ours. To rephrase the saying of A.
Clarke, sufficiently advanced civilizations are indistinguishable from nature.
