This is certainly incorrect. It *is* widely believed
that Soviet texts
dating prior to 1973 (when the USSR became party to the relevant
convention) may be freely used and considered public domain, but this is
almost certainly untrue from a legal standpoint, and copyrighted
material produced subsequent to that date is as protected as this
message (moreso, perhaps).
The relevant US law is Title 17, Chapter 1, Section 104
http://www4.law.cornell.edu/uscode/17/104.html
In essense, if the work was first published in a country which was not a
party to a copyright agreement with the United States at the time, it is
mostly likely not covered under US copyright law. Note that I only say most
likely. I'm not a lawyer, and I'm not going to get into the nitty gritty
details and exceptions. Also, the laws of other countries will likely
differ.
Anthony