Terrorists will not strike are similar targets twice - They will do something completly diffrent and unexpected

It is highly likely that this report is spurious, as were previous such reports over the past five weeks. First, the pattern of its distribution is inconsistent with the normal means by which credible threat reports are disseminated – namely, via national and international security entities, who in this case have not received any such information. The likelihood that a non-governmental source would have a credible report of a major kinetic operation is very close to zero.
More fundamentally, it is highly unlikely that al Shabaab would attempt another complex operation in Nairobi akin to the Westgate attack in the short to medium term. As a result of the attack, much pressure has been exerted on HSM networks in Kenya (which would have been expected) by Kenyan security agencies, and the national government is more generally operating on a higher state of alert at the moment.
This implies a significantly higher likelihood of failure for any large operation in Nairobi. As such, the government is not expecting such an operation, and is instead mostly primarily focused on the possibility of smaller kinetic activity – mostly in eastern Nairobi – that would demonstrate presence but be less likely to be disrupted.

@masukuma you are right shabbab is under pressure from all directions aljazeera is reporting its director of suicide missions has been "droned" near kismayo...

Jurgen Warmbrunn: Trouble with most people is that they don't believe something could happen until it already has. It's not stupidity or weakness, it's just human nature.
Gerry Lane: How did you know?
Jurgen Warmbrunn: Gerald Lane, the self defeating Jeremiah, model employer in the U.N., back in 2010. Caused a few ripples, sidelined your career. Thought you'd have parleyed those ripples into a self-righteous book.
Gerry Lane: No one does for profit. How did Israel know?
Jurgen Warmbrunn: We intercepted a communique from an Indian general, saying they were fighting the "rakshasa". Translation, "zombies". Technically, undead.
Gerry Lane: Jurgen Warmbrunn, high-ranking official in the Mossad. Described as sober, efficient, not terribly imaginative, and yet, you build a wall because you read a communique that mentions the word "zombie"?
Jurgen Warmbrunn: Well, if you put it like that, I'd be skeptical as well.
Jurgen Warmbrunn: In the '30s, Jews refused to believe they could be sent to concentration camps. In '72, we refused to be massacred in the Olympics. In the month before October 1973 we saw Arab troop movements, and we unanimously agreed that they didn't pose a threat. Now, a month later, the Arab attack almost drove us into the sea. So, we decided to make a change.
Gerry Lane: A change?
Jurgen Warmbrunn: "The tenth man." If nine of us with the same information arrived at the exact same conclusion, it's the duty of the tenth man to disagree. No matter how improbable it may seem, the tenth man has to start thinking with the assumption that the other nine were wrong.
Gerry Lane: And you were that tenth man?
Jurgen Warmbrunn: Precisely.
Jurgen Warmbrunn: Since everyone assumed that this talk of zombies was cover for something else, I began my investigation on the assumption, that when they said, zombies they meant zombies.