Okay, thank you. Unfortunately, I do not have good news; but, all I can do is be honest... The problem you are seeing is caused by "stuck" mirrors on the DMD (digital micromirror device) in the optical engine. I have seen this problem on Mitsubishi and many other brands of DLP TVs, as well.
Each spot (pixel) that you view in the picture is made by a single mirror moving back and forth on the DMD. In total, there are over a million of these tiny mirrors, and the white spots you see are those mirrors that have stuck "On." I borrowed a photo from the internet to help show what happens on the DMD:
To correct this problem the optical engine in the TV must be replaced. However, the repair cost is quite high: The Mitsubishi replacement retails for $1014.10, plus shipping, tax, and labor. Usually labor is in the $200-300 range (in my area). If needed, the part number for the optical engine is: 938P075010. You may be able to find less expensive optical engines on the internet, but these engines could be a gamble, so please use caution if shopping for a lower price.
I recommend contacting Mitsubishi Consumer Relations at(NNN) NNN-NNNNto ask (emphatically insist) that they cover the cost of the repair. They may very well supply the optical engine at no charge, with you paying the labor; but, it doesn't hurt to keep trying for the labor cost, too. Please remember you paid a premium price for a premium brand TV that has lasted less than three years(!). You may need to be insistent, and make several calls, but Mitsubishi is well known for being very helpful (hint).
Important: Usually Mitsubishi requires one of their authorized servicers to check the TV on-site first, before they will offer a concession (even though they will already know exactly what is wrong with it). It is best to have an estimate of the repair from the technician before you call Mitsubishi.
If needed, your nearest authorized Mitsubishi servicer can be found by entering your information on this page:
I know this is not good news, but it is the truth. Please let me know if you have any questions, or if I can help in any way.