Racist Spam

Got to the office, sat at the comp, checked office's e-mail... then checked my own private e-mail and there it was: Spam.
Two messages had arrived into my inbox from someone I don't know, with a subject line that surprised me "Trotz Stellenabbau".
It's been some (long) time since I had to give up my German classes due to lack of money but I still remembered enough to understand it, and I did know it was nothing I could be mailed about.
This is a virus's doing.
Actually, the message itself isn't a virus, but this is the result of viral activity.

You can read more about it here. Basically, this is malware that, behind your back, starts sending spam e-mail. The virus spoofs the sender email and uses a random address from a list of e-mail addresses it has retrieved from an infected computer. So, in simple words, the mail looks like it's been sent by someone that you might know (or not) but in truth it's been sent by someone else.
For this reason just blocking the sender's address (like Yahoo! mail lets you do) will just not work and you will be probably blocking out someone who has nothing to do with this. Their e-mail address just happened to be in a list some spammer happened to come by; and now it's being used to make it look as if they were sending spam, which they probably aren't.

Read the article I linked above, and if you are using an e-mail application such as MSOutlook go shoot yourself in the head follow the instructions here to block the real sender of such spam. After you've done so, please do yourself a favor and download a better tool for reading and sending pop3 email: Thunderbird. Thunderbird will import your address book and old messages, so that you can seamlessly switch.

Aside from this, remember to keep your antivirus updated. If you think an antivirus application is too expensive, you can always use free alternatives which are just as good and effective.

Avast!
AVG antivirus
are two good examples. (there are others)
Additionally, you might want to try free online-scans services that both panda-antivirus and symantec offer in their websites.

You know this is important because of many reasons:
1) Viruses put your privacy at risk. A virus can not only wreck the data kept in your computer, it can also "steal" sensitive information about you and steal your identity. After it has done so, it can go and put your home on a mortgage, buy an expensive car at your expense, or commit online crimes that would all point towards you. You will have a VERY tough time trying to prove it was not you who did these things and chances are you/your family will lose a lot of money while at it.
2) Viruses attack your friends. If you don't give a shit about your personal security or finance, you might perhaps care about your friends.
3) Your computer being a zombie means your computer no longer belongs to you. Since your computer is in your home, it means you have just let someone in.
4) Your ISP might trace malicious activity to your zombie machine and decide they no longer want to give you internet access. Your ISP (Internet Service Provider) might just decide to take their service away from you and you'll have no way to go online.