They are referring to the scores of Somali former refugees who grew up in the West (in Britain and the US) and have returned to Africa for Jihad training with Al-Shabaab.
From the Sydney Morning Herald:
A NEW wave of battle-hardened ”lone wolf” terrorists is expected to infiltrate Britain and the US from African and other war zones to carry out attacks, according to security experts.
British and American Somalis currently fighting alongside Islamist rebels in Somalia are expected to pose a serious threat upon their return from Africa, training others in the techniques they learnt on the battlefield and in terrorist training camps.
”It is only a question of time before their commitment to the cause, and their newly acquired expertise, are likely to be seen on British streets,” says the Royal United Services Institute, a London-based defence think tank.
RUSI, in a report titled The Global Origins of New Terrorism, says about 50 fighters with the Islamist group al-Shabab, which is affiliated with al-Qaeda, are from Britain.
They say the new terror threat will also come from Islamist fighters returning from wars in Yemen and Nigeria, and from the renewed violence in Iraq.
The predictions are echoed by the controversial chairman of the US House committee on homeland security, congressman Peter King, who has warned of the threat to the US from an estimated 50 American Somalis fighting with al-Shabab.
That number (50) is a lot higher then we’ve seen before, but then since the media first got wind of all this back in 2008, our homeland security people might be staying mum now not wanting to scare the public.
The story goes on, here. Note that King mentions a study which concludes that 80-85% of US mosques are radicalized.