If I read it correctly, they used the binary compiler which existed on the machine to compile a new copy of the compiler (from clean source). This existing bina

If I read it correctly, they used the binary compiler which existed on the machine to compile a new copy of the compiler (from clean source). This existing binary compiler was "poisoned" (modified) such that it would not only poison the psychiatrist's program, but also poison any attempts to compile a new copy of the compiler. So when they recompiled the compiler, the new copy was already poisoned (because they used the old, poisoned compiler to do it).