Most of us get spam trying to sell us things, most commonly prescriptions, cheap mortgage rates, online gambling and other, more “adult” topics. Most of us just delete them or hit the “spam” button and move on. There are some other types of spam that are a little more serious, however.

One of the most common ones has been around for many years - the Nigerian bank scam. The person sending the email pretends to be the wife, brother, lawyer, banker or have some other relationship with some kind of government official in Nigeria. They tell the sad story of money that was deposited in a bank account but can’t be accessed because the person has died. They offer to give you a share of the wealth in return for accepting a transfer of the money to your bank account. The catch is, you need to give them your bank account information and transfer several thousand dollars to them first for “expenses”. Naturally, you never see any of the money that is promised after sending the expense funds. It sounds obvious, but people fall for this scam year after year, even though it has been going on for so long.

Other scams offer investments with huge paybacks. They always claim to be risk-free naturally, but once you’ve sent them your money it’s highly unlikely you’ll ever see any of it again, let alone profit. A similar scam involves credit cards for people with poor credit ratings. You send them a security deposit and processing charge and they send you a credit card. Unfortunately, once they have your fees you’ll never hear from them again.

These fake offers are particularly bad for legitimate businesses who use email for doing business. Because so much email is spam, the internet service providers and email hosting companies work hard to filter it out. But these filters can sometimes stop legitimate email from businesses you want to hear from.

How To Sidestep These Scams

First, never reply to spam. This just tells the spammer that your email is in fact valid and the amount of spam you’ll receive will quickly multiply. Some spam will even include a link at the bottom for removing yourself from their list. If it’s a true spam email, don’t use this - it just confirms your email address as well. If you did sign up to receive the email however, this is a legitimate way of removing yourself from future mailings.

Above all, never give your credit card number, bank account details or private data to anyone unknown over the Internet. PayPal, for example, and other legitimate online businesses will never ask for your password in an email. One common scam is to fake return addresses and tailor subject lines and content so the message appears to be from them or another financial institution ‘confirming’ your information. Don’t fall for them.

How do you know whether it’s spam? Since, one man’s spam is sometimes another’s welcomed advertisement, there’s no perfect answer. But there is one good rule of thumb: if you don’t recognize the sender, it’s probably not someone you want to hear from. After all, how many former dictators in Nigeria are you likely to know?