Spurious emails being sent to people on my contact list

We discovered today that spurious emails are being sent to people on my wife's email contact list. I contacted the Microsoft support desk and was led through a process to reset her account password because I was told that somebody had probably hacked into my wife's email by having her password. I'm dubious whether this will resolve the problem by itself. Is there anything else which should be done to avoid a recurrence of this issue? I am already carrying out a full system scan of our computers.