Russians possibly hacked 20 ships' GPS in the Black Sea [Translated]

Perhaps it is not intentional hacking:

As far I remember GPS signals are incredibly small (-120db). Actually tests were made by the FTC, when a Telco (LightSquared) asked to use for satellite usage, a frequency band reserved for terrestrial usage (LTE). Those tests shown how GPSs become easily erroneous if there are more powerful radio sources in vicinity, that use close frequencies.