 The USPTO opened an investigation and concluded by rejecting all claims in the patent.The next year, the USPTO further announced that following the re-examination process, it affirmed the rejection of '517 and additionally found U.S. patent 5,758,352 invalid on the grounds that the patent had incorrect assignees.However, in 2006 the USPTO ruled that features of Microsoft's implementation of the FAT system were "novel and non-obvious", reversing both earlier decisions and leaving the patents valid.