Format of updates

Sounds like a plan... 

I've clicked 'not now' more than 3 times.

Either you are in error or it's fake.

If fake, how do I get rd of the notification for good?

If after the necessary 3 refusals required for an AT&T forced update, no update was made, I recommend this:  Write down the following info so you have a record:  the # the message came from. the date+time you first got it, & exactly(word4word) what the message said, then type in all caps, "STOP!",  and send the reply. Then IMMEDIATELY(!) DELETE the conversation thread anywhere that it may exist like if you have your phone set to automatically "backup & restore" to the cloud or Google Drive, whatever...you should be sure to eliminate it from everywhere because it's just the "link" a hacker needs to get whatever information they need. Blocking the number couldn't hurt either although they usually just use a different number each attempt.

 As someone who's had their identity stolen 3x's (yes, THREE TIMES!!) I can assure you that a breach of your personal information is (VERY) possible through text messaging. I've been "robbed"(for lack of a better word) via Fbook, Phone, and good old- fashioned driver's license copying.  This all started in 2012 and even though I've been working with the FBI, USDOJ, & Homeland Security(it's considered a terroristic threat against the America's Economic Stability when done over the internet) I'm still dealing with new issues on a weekly basis and was astounded when I learned that by leaving a text message or email(after opened) just sitting on your phone/PC, you're giving the hackers all the time they need to "break-in" and access your information.

After you do all this, you can go into your phone's settings to check for any available updates, after that though,  please do the world a favor and go to the website: https://complaint.ic3.gov/default.aspx   and report the incident to the Feds. This is another reason I suggested writing everything down word for word. You might not think it's a big deal but think about it...you're probably NOT the only person getting this message and someone else might not stop to consider the "WTHuh?!" for getting it and think to ask someone before just hitting that install prompt. Nobody (and I mean NOBODY!) believed me when I first told them about reporting the "cyber crime"  to the FBI but just this past June I received notice from the USDOJ in Norfolk, VA that  by using the information I provided,(along with several other victims), not only were they able to track down,  arrest,  and prosecute the 7 individuals doing the hacking but I was being awarded a small reward for providing information leading to their arrest & conviction, so I truly hope you take my recommendation seriously ESPECIALLY the delete and block part. The things some people can use computers for is utterly astounding, to say the least, and if they would use these powers for good instead of evil, the world would be a much happier place.

Good Luck and thanks for sharing, now we are aware of yet another way someone is trying to gain at the expense of another., by asking for confirmation you saved yourself years of possible aggravation and frustration, be glad..