It is the name for perhaps the most powerful piece of spyware ever developed – certainly by a private company. Once it has wormed its way on to your phone, without you noticing, it can turn it into a 24-hour surveillance device. It can copy messages you send or receive, harvest your photos and record your calls. It might secretly film you through your phone’s camera, or activate the microphone to record your conversations. It can potentially pinpoint where you are, where you’ve been, and who you’ve met.
In 2019 WhatsApp revealed that NSO’s software had been used to send malware to more than 1,400 phones by exploiting a zero-day vulnerability. Simply by placing a WhatsApp call to a target device, malicious Pegasus code could be installed on the phone, even if the target never answered the call. More recently NSO has begun exploiting vulnerabilities in Apple’s iMessage software, giving it backdoor access to hundreds of millions of iPhones. Apple says it is continually updating its software to prevent such attacks.
So best you can do is make sure your OS is as update to date as possible (a problem for older Android phones) and yes be careful what software you download, and from where.
See What is Pegasus spyware and how does it hack phones?
NSO Group software can record your calls, copy your messages and secretly film you