Why is the fan on my computer always running?

I’m not a tech-person per se but from time to time friends and family ask me to help them out with their ‘computer problems.’ Recently a friend told me that her laptop fan was always running. She had been told by a local tech store the fan was to protect her laptop from over-heating, which is true, but my friend still thought it weird that her fan was constantly running.

My friend said that the fan would start up as soon as she started her laptop in the morning and it would stay on almost all day; surely, she reasoned, the laptop can’t be hot at the beginning of the day, can it? She asked me for my thoughts and I asked her three questions in return:

  • Has your electricity bill increased?
  • Has your network slowed down?
  • Has your CPU usage spiked? (CPU is like the ‘brains’ of your computer)

And then I explained cryptojacking to her.


Crypto mining is hard and hot work and takes a lot of electricity. And as a result, people’s electricity bills skyrocket when they mine for cryptocurrency on their devices. However, some people don’t want to spend money on electricity so they steal other people’s electricity, which is obviously illegal. When crypto mining is done illegally in this way it becomes the crime of cryptojacking.

Cryptojacking is similar to taking over someone’s vehicle in a carjack; cyber-crims break into and take over someone’s network where they install cryptomining software onto their victim’s computer. Then, unbeknown to the victim, their computer begins mining cryptocurrency on behalf of the criminal. The victim, however, does not receive any currency in return, just a slower computer and a higher electricity bill!

The criminal ethos behind cryptojacking attack is very simple: the more CPUs you have mining for you, the more money you make. And, if a criminal can access your electricity and CPU the less of their money they have to spend on mining coin.

Avoiding cryptojacking

Cryptojacking has become a serious global problem as many people can be easily targeted. Some ways to avoid becoming a cryptojack victim include:

  • Protect your devices from Malware and ransomware attacks with products such as Malwarebytes or Kaspersky Lab
  • Keep your devices updated and patched to minimise the risk of exploit-related attacks
  • Be wary of using public/guest WiFi as the Host may be infected
  • Use a cryptocurrency miner blocking software if you are not legitimately mining cryptocurrency
  • Use AdBlocker (I have this). Or if you don’t want to use an ad blocker or just want to specifically block coin mining, here are some other suggestions:
  • Disable JavaScript on specific sites – or ask a techie to do this for you. (The problem, with this, however, is that this is a very aggressive way to block mining and will break many websites. Facebook, for instance, will not load without JavaScript enabled).

Solving my friend’s problem

After some careful analysis of my friend’s low electricity bills, low CPU usage history, and her very slow laptop burning the midnight oil, aka her fan, we came to the conclusion that her 2007 Toshiba Satellite Pro running Windows XP was the problem and not the result of any cryptojacking!

Sophos, CNet



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