I started and grew a technology company in the late 1990s, and sold it after being approached by a larger, public company. From letter of intent to closing it took about six months and during that time I let the employees know what was happening. Would I do that again? No, I wouldn’t, and I recommend to my clients now that they think carefully before letting their employees know.
http://www.allbusiness.com/labor-employment/resumes-curricula-vitae/12354189-1.html
Key, trusted employees are different, and it can be very helpful to have them on your side in an acquisition. Often an acquisition means growth opportunities for them, so it doesn’t hurt to let them in on your plans. Just let them know how important it is not to discuss the plans with other employees.