Moscow delivered "bursts of bad weather" but China was responsible for "changing the climate" of security and intelligence, the new head of MI5 Ken McCallum said.
The U.K. is experiencing some of its highest crime rates in decades.
Suicide bomber Abedi was one of 20,000 people known to MI5 but not one of the 3,000 people under active investigation.
A British-born convert to Islam, Masood had racked up a string of convictions, but none for terrorism-related offences.
A Spanish double agent did everything he could to stop his wife from blowing his cover.
International cyber crime groups are advancing faster than agencies can put up defenses.
A poll shows many voters think the government is working with MI5 to rig the referendum.
John Sawers and Jonathan Evans write that a withdrawal vote would hurt the EU and leave Britain vulnerable.
In a rare public speech, the head of MI5 Andrew Parker warned a strike on the United Kingdom was highly likely.
Former CAPO agent Uno Puusepp has been unveiled as a double agent for Russia's FSB
Britain's security services have for years been accused of colluding in the ill-treatment of suspected militants.
A parliamentary committee said that a U.S. communications firm could have led investigators to head off the plot
MI5 and other security services are on red alert for 'thousands' of potential domestic terrorists in the capital, say insiders