Since you only use the account from the AOL page, it is very unlikely that it is anything on your computer. Also, even if someone hacked into your linux system, which is pretty unlikely, it's also pretty unlikely that they would choose to access AOL rather than the many other things they could do.

What is not at all unlikely is that someone simply managed to barge into your AOL account, since AOL has lots of users, and is often used by people who know little about strong passwords, and so is not that hard to get in. Also, there are a lot of abandoned AOL accounts that can be used for a longer period of time than an active account.

Do you run any servers that are open to the outside world? If not, I wouldn't worry.