What did attackers break into?

Qatar National Bank's databases, breaching 1.5GB of data.

How did the attackers break into it?

It is not exactly known, but it could be done by employing phishing campaigns or spreading malware to target specific employees.

Who was impacted?

Financially speaking, none of the customers. However, QNB's reputation got affected and many started considering moving their funds.

How was it investigated?

QNB is still investigating the breach. Third parties were also involved. Bozkurt Hackers, a Turkish hacking group, shared a video on social media claiming to be the group behind the breach.

Turkish hackers claim responsibility for Qatar national Bank breach | Trend Micro (PL). (n.d.). https://www.trendmicro.com/vinfo/pl/security/news/cyber-attacks/turkish-hackers-responsible-for-qatar-national-bank-breach

Qatar National Bank Investigating Alleged Data Hack | Reuters. (n.d.). https://www.reuters.com/article/idUSKCN0XO22S/