Ransomware is malware which silently encrypts your files in the background. There are no immediate markers of this except continual HDD use even when idle or extreme CPU load at all times. Once complete, a pop-up will appear demanding payment (usually in Bitcoin) in return for the decryption key. Decrypting without this key is practically impossible.
Although the most high profile cases right now are against NHS machines, this is not a targeted attack and can affect any system via email or via direct connection to large, exposed networks.
To secure your system, if you are using Windows:
– Ensure it has been updated to Windows 10 and the latest security patches have been applied. Those using XP should upgrade immediately without question.
– Avoid opening email attachments wherever possible. Best practice is to avoid sending emails with attachments and persuade your family and friends never to send you any. Use Dropbox or other cloud-based solutions instead.
– Ensure Windows Defender is enabled and up-to-date. If you are very cautious Bitdefender is my recommended 3rd Party solution which would also have prevented this attack.
– Finally back up your data regularly to disks which are not connected to the computer at all times (these ransomware attacks seek out and encrypt your backups as well if they can find them!).
macOS users should be aware that, although this prominent attack does not affect macOS, improperly run macs are not immune to ransomware and I would always advise using the default security settings to avoid allowing potential malware to execute on your mac.
If you open an email and realise it is likely to be malware, the very safest thing to do is to shut down your machine, remove its Hard Disk Drives and connect them to another computer as secondary disks. You should then copy your important data off them onto a clean machine. This is obviously an extreme reaction. The safest thing to do is to keep regular offline backups of your important data.