Factual:
ADS-B position data is coming directly from airplanes. There is nothing like inaccuracy, although position quality may be less than RNP-1 for certain airframe/equipment combinations.
Bashing this system is nonsense when it is the only source of data that is available at this time.
FR 24 is not a Russian website, but Swedish and well reputated in my eyes.
More factual:
Aircraft disappeared at 17:22Z from FR24. This may be due to
a) lack of further transmissions for whatever reason
b) failure of ground receiver, however other aircraft where continued to be received
c) failure of FR24 network and server processing
Aircraft had just passed IGARI waypoint and turned right from track 025. Last reported track was 040. If it was to follow M765 it should have turned to heading 058 (can't say what track, don't know variation in the area), but there may be direct routing by VVTS involved. Others flying there will know more.
https://www.dropbox.com/s/se1myn0lvjmd7u7/igari.jpg
Last reported FR24 position is N6.97 E 103.63
This equals to N6 58' 11.99" E103 37' 47.99"
FR24 data shows the following sequence (note that ADS-B sends positione about 1 per second, but FR24 consolidates these data to about 1 per minute. Further visible movements of the aircraft are due to FR24 forecast algorithm)
https://www.dropbox.com/s/q15ip8rwr6mgj9x/mas370.avi
UTC LAT LONG GS TT FL
17:13 6.00 103.14 472 025 350
17:15 6.13 103.20 472 025 350
17:15 6.24 103.26 472 025 350
17:16 6.36 103.31 472 025 350
17:17 6.48 103.37 472 025 350
17:18 6.58 103.41 472 025 350
17:19 6.68 103.46 472 025 350
17:20 6.80 103.52 472 025 350
17:21 6.93 103.59 471 040 0
17:22 6.97 103.63 471 040 0
Indication of an altitude of 0 may result from a variety of circumstances depending of the type of Mode-S/ADS-B packet received. FR24 will likely know more because it has much more packets and the type of packets received.