Blackmail fears were raised in June when hackers tried to break into the system used by MPs, peers and staff by searching for weak passwords.
Investigators have traced the source of the attack to the Tehran regime, according to reports.
The immediate suspicion fell upon foreign governments such as Russian Federation and North Korea, both of which have been accused of coordinating previous hacking attempts. An NCSC spokesperson told the Times: "It would be inappropriate to comment further while enquiries are on-going".
There is an ongoing investigation into the incident by the National Cyber Security Centre (NCSC) and the National Crime Agency.
The timing is potentially hard; the revelation comes shortly after Britain's Prime Minister Theresa May, along with other European leaders, issued a strident defense of the 2015 nuclear deal between Iran, the USA and other powers, in the face of new attacks on it by President Donald Trump.
An Iranian man reads a copy of the daily newspaper "Omid Javan" bearing a picture of US President Donald Trump with a headline that reads in Persian "Crazy Trump". "May's response to Mr. Trump".
In a rare joint statement, May, Germany's Angela Merkel and France's Emmanuel Macron said the nuclear deal was in their countries' "shared national security interest" and said that they remained committed to the agreement "and its full implementation by all sides".
"We encourage the U.S. Administration and Congress to consider the implications to the security of the U.S. and its allies before taking any steps that might undermine the [nuclear deal], such as re-imposing sanctions on Iran lifted under the agreement", the European leaders said.
"The nuclear deal was the culmination of 13 years of diplomacy and was a major step towards ensuring that Iran's nuclear programme is not diverted for military purposes".
"It was not the most sophisticated attack but nor did it need to be", a source told the Times.
She said: "It is an act of wanton vandalism for Donald Trump to jeopardise the future of that deal today, and to move the goalposts by linking it to important but utterly extraneous issues around Iran's wider activities in the region".
"Yet sadly, this kind of reckless and thoughtless behaviour is what we have come to expect from this president".