There are some who question the origin of the design of the Soyuz capsule - See "Was the Soyuz Design Stolen?" http://www.astronautix.com/articles/wastolen.htm for more details.
Per the above Astronautix.com article:
The General Electric Apollo D-2 / Soyuz Design Concept
The fundamental concept of both designs can easily be summarised as obtaining minimum overall vehicle mass for the mission. This is accomplished by minimising the mass of the re-entry vehicle. There were two major design elements to achieve this:
Put all systems and space not necessary for re-entry and recovery outside of the re-entry vehicle, into a separate jettisonable 'mission module', joined to the re-entry vehicle by a hatch. Every gram saved in this way saves two or more grams in overall spacecraft mass - for it does not need to be protected by heat shields, supported by parachutes, or braked on landing.
Use a re-entry vehicle of the highest possible volumetric efficiency (internal volume divided by hull area). Theoretically this would be a sphere. But re-entry from lunar distances required that the capsule be able to bank a little, to generate lift and 'fly' a bit. This was needed to reduce the G forces on the crew to tolerable levels. Such a manoeuvre is impossible with a spherical capsule. After considerable study, the optimum shape was found to be the Soyuz 'headlight' shape - a hemispherical forward area joined by a barely angled cone (7 degrees) to a classic spherical section heat shield.
This design concept meant splitting the living area into two modules - the re-entry vehicle, with just enough space, equipment, and supplies to sustain the crew during re-entry; and a mission module. As a bonus the mission module provided an airlock for exit into space and a mounting area for rendezvous electronics.
The end result of this design approach was remarkable. The Apollo capsule designed by NASA had a mass of 5,000 kg and provided the crew with six cubic meters of living space. A service module, providing propulsion, electricity, radio, and other equipment would add at least 1,800 kg to this mass for the circumlunar mission. The General Electric D-2 or Soyuz spacecraft provided the same crew with 9 cubic meters of living space, an airlock, and the service module for the mass of the Apollo capsule alone!
The modular concept was also inherently adaptable. By changing the fuel load in the service module, and the type of equipment in the mission module, a wide variety of missions could be performed. The superiority of this approach is clear to see: the Soyuz remains in use 30 years later, while the Apollo was quickly abandoned.
General Electric Apollo D-2 design; Image from The Unwanted Blog on up-ship.com