Like spam and phishing mails, hoaxes attempt to win your trust by referring to well known, recognised institutions. The apparently factual information is typically presented as sensational and urgent, for example by warning you of particularly dangerous malware.

One obvious thing is missing however: times and dates are nearly always omitted. Instead, the text of the hoax suggests that the made-up event is taking place right now. It uses words like 'yesterday' or 'just recently'. These words can of course appear to refer to the present a week, a month or a year later. Sometimes, hoax e-mails contain promises of a reward or bonus if you forward the e-mail. Or, they promise you'll earn lots of money.

Five alarm bells for false reports

• 'You must tell all your friends': you'll be asked to forward the hoax to as many colleagues, friends and family members as possible.
• The subject line includes the word 'warning'.
• The message describes highly exaggerated possible consequences of, for example, a computer virus that the hoax also mentioned in the mail.
• Well-known companies or organisations are often mentioned as proof of what the hoax is claiming.
• However, the author of the hoax does not announce their identity.

Can a hoax really be dangerous?

A hoax become dangerous for you if you follow any instructions in the mail. For example, a hoax might 'recommend' that you delete a file on your computer. The hoax authors may claim that you need to clean up your system after a made-up malware infection. In truth the file named is a vital system file without which your computer won't function properly. If something like this happens on a company computer, the IT department will be saddled with extra work. And the affected employee will not be productive until the problem is fixed. Hoaxes can cause economic damage just from the time and attention they monopolise: if thousands of employees at one company each spend three minutes reading a chain letter and forwarding it, this adds up to a loss of 50 hours of working time. In addition, the reputation of companies maligned in hoaxes may be damaged massively. They may lose both face and money.

Hoaxes that spread false reports may cause more than economic damages: the democratic process of publicly forming an opinion could also be impaired: critics of climate and vaccines as well as other conspiracy theorists use 'alternative facts' to gain political influence. Extremist movements utilise hoaxes to divide public opinion.