How Google Site were tried to hack ?

I was searching for the analysis report how Google accounts were tried to hack. Hackers objective was trying to get full permission on google users accounts, and to get the email contents from user accounts.

Suspicious emails were sent to large number of user accounts with from address as well known address.
Ex:  To ABC email account, suspicious email sent as from XYZ, here  XYZ is well known sender to ABC. Here, I am not clear how hackers got well known from address for different user accounts.

Malicious software were attached these suspicious emails. When users accessing or opening these email, mallware package would have executed , will start running from user system.

These mall-ware installable will read the users cookie and other valid information. Hackers were these vital info to access google accounts or email contents whenever users accessing .