Just got notified from hotmail that my account had been blocked

Among the reasons given as to why my account was blocked was because it had been reported for spam/junk. Upon confirming this with my brother I was able to see that he had received junk mail (stuff like "re: 9" etc.) from my hotmail account; I did not send these messages. He had a total of two such messages from my account.

This leads me to believe that someone else accessed my account. I am unaware of what to do next. A few months ago, I noticed that I kept getting pop-ups, and installed spybot search and destroy. Using the program, it detected 11 counts of adware. Upon attempting to fix them, I was notified that only 9 of the 11 problems were fixed. Additionally, any scan after this point always affirmed that there were no further threats detected. I have several questions in relation to this.

• Could this past problem from months ago explain how my account was accessed? Spybot did not identify it as malware or anything, only adware. I recall seeing "coupon" as part of the description, perhaps that was the company responsible, unfortunately I cannot fully recall the details of the scan apart from the fact that 9 of 11 problems were fixed.

• As well, what ever came of the 2 problems that could not be fixed? Is there a reason spybot has not detected these problems since the first scan? My limited knowledge in this area leads me to assume that an unfixed problem would only continue to be detected in each scan for as long as it is unfixed, however, the problems have never turned up again. Could they be responsible for the activity of my email? As well, I was never able to detect any problems from spybot from this initial scan, although ads continue to pop up every now and then.

• After changing all of my passwords on things, I ran another scan in spybot and it detected no problems, which has been the result since it fixed the 9 of 11 problems on the initial scan. Despite this result, there is clearly something wrong going on here. What could it be?

Can it be the case that apart from adware issues, there are also malware issues or keylogging going on that has not been detected? Is changing passwords an effective way of combating this sort of thing at all or will it only happen again after some time? How can I fix this? Any help is greatly appreciated.