SharePoint 2010 Web Analytics showing user Display Name and Account Name from the same user

Hi!

Since July, 16th 2012 the Web Analytics Daily Unique Visitors reports started to show almost the double of visitors we used to have on our Web Application. Here are some of the data (I intentionally deleted the weekend data):

10/7/2012 2.497
11/7/2012 2.723
12/7/2012 2.722
13/7/2012 2.699
16/7/2012 5.055
17/7/2012 4.963
18/7/2012 4.954
19/7/2012 4.998
20/7/2012 4.965
23/7/2012 5.117
24/7/2012 5.012
25/7/2012 5.071

As you may notice the data jumped from around 2.700 unique visitors to around 5.000 unique visitors. As the number of permissioned users remains constant it is pretty odd. I also checked the Number of Page Views report and see no change on its behavior. The number of page views remained constant.

So I went to look the Top Visitors report and understand why the visitors number almost doubled. The analytics started to count the users Display Name and Account name as two different visitors with a different number of page views. Let me show you an example from yesterday (July, 25th) Top Visitors report:

#     Visitor                  Page Views    %
1    Cinthia XXXXXXXXXX    359        0,55%
5    Giselle XXXXXXXXXX     143        0,22%
7    Aline XXXXXXXXXX       138        0,21%
15  nt\cmazevedo              111        0,17%
60  nt\gbsantana                 69        0,11%
73  nt\aglsiqueira                 65        0,10%

"Cinthia" and the account "nt\cmazevedo" are the same person. The same is applied to "Giselle" / "nt\gbsantana" and "Aline" / "nt\aglsiqueira".

As I stated this is an example from July, 25th. If I checked the same report from a period before July, 16th I can only see the users Display Name as "Visitors". No account name is displayed or counted as a different visitor.

About the environment:

We have two SharePoint 2010 farms: a "corporate" and a "enterprise". The corporate farm contains four web servers and a central administration servers with publishing services. The enterprise farm contains two servers running User Profile Services, Search Services and some others. Our main version is the SP1 with June/2011 Cumulative Update with a few more hotfixes applied.

This behavior on analytics is affecting all web applications (we have more than 20) installed on this farm and my company Support team said that no change were made on SharePoint on the weekend the problem started.

Does anyone have any tip about what is going on?

Thanks in advance!