Penny Stock Scams
Such scams typically run by phones, but also could appear in emails or mails. It uses your human nature greed and tips you some never heard of companies which will jump 100% in next week or so.
Such obscure companies, or so called "penny stocks" are the investment equivalent of throwing money down the drain. They are usually thinly traded, highly volatile, and priced at a penny or even less. Tipsters from never heard of brokerage firms will tell you some "insider" information that will make the penny be dollar in a short period of time. The key is you need to jump in right now, otherwise you will regret the rest of your life!
Well-known brokerages, such as Fidelity or Schwab, do offer access to very small stocks, but they often take great pains to qualify investors in advance of such risky trading.
Retirement investors should take a big step back, unless you really want to go back to full time employment soon.