Wikipedia (unfortunately, sourcing a print book so I can't vouch for its having been quoted fairly) indicates Soviet agents were definitely stealing Concorde plans during the Tu-144's development.
I'm, of course, interested in arguments with some base to them. Wikipedia marks the section as "disputed" and mentions that stolen (if) were the preliminary designs.
Again, you have to know a lot to have use of plans like that - especially when the design is a moving target.
