In order to access the Internet, you have to be a part of it. Your Internet Service Provider assigns you an address much like the Post Office. Some addresses are dynamic (they change from time to time) and some are static (never changes). When you transmit data, such as an email, your IP address is attached to that data. When it hits Internet routers, it reports where the data came from, what's in it and where it's going.
If you ever catch a computer virus or malware, one of the symptoms may be to turn your computer to what we call a zombie.
So what do you do now? Well, you could just ignore it. If you're using web based email you wouldn't even notice. But I digress, because I wouldn't have gone through the trouble of a long and elaborate blog entry just to tell you to ignore your problems.
Step 1: Zombie Killing
Put down the pitchfork and torch. What you need is an antivirus and antispyware solution. There's a few available for free online. I'd recommend a combination of the two.
Step 2: Checking the Blacklist
You can actually check to see if your blacklisted by going here. If you find that you are you're going to have to apply to every site you are blacklisted on to be removed from the list.