A harmful virus, spyware, spam, spoofs, trojans, chain letters, child porn, or just advertising for those "male" enhancements... Why would anyone even think E-mail would be a good idea?
Given the rate at which all of the above show up in your Inbox, you may be wondering just that. Thankfully some ISP's are having some success with filtering software to keep a lot of the above from reaching you or your kids. However, you can't always depend on filtering software.
If you don't know for sure who the e-mail is from... DO NOT click on ANYTHING in the message. And you have to keep mind that sometimes e-mail is forged to appear to come from someone it didn't. Some viruses actually use a person's address book to resend itself to all the person's contacts. You should probably check out additional filtering software, but the general rule of thumb is be suspicious... very suspicious of e-mail.
E-mail can be a very useful tool, I use it pretty much everyday, and sometimes wonder what I did without it. But there is a lot of bad to go along with the good, and you have to be careful.
Spoofs (forged e-mail made to look like it came from E-bay, Paypal, etc.) are devised to convice the victim that they are legitimate to trick the victim into supplying information, usually credit card information, so that it can be used fraudulently later. These are usually very convincing in appearance, and often actually include the company logo and real quick links to the legitimate site to help convince the victim. They usually claim that your account has been suspended or that their records need to be updated and that your use of their service will be denied if you don't follow their link and supply the requested information. Don't fall for it. Those companies do NOT send out e-mail like that, and anything you need to do to your account can be done safely by going directly to their website, and not through a link in an e-mail.
If you encounter some type of criminal activity using e-mail and want to report it, be sure to save copies of ALL of the messages from the person WITH the full headers still attached. You should also print out the messages with the headers still attached to have them ready for local law enforcment. The full headers will have information that can help investigator track from whom the e-mail originated. If you don't know how to work with headers, read up on it in the help section of whatever mail software you are using. Sometimes it's just an option that is clickable at the top of the message.