You may need to consider TenFourFox browser because it is up to date.
Safari is not. Ten Four Fox is a mozilla derived custom build for PPC Mac.
You can choose another browser as system default within Safari preferences
so that is one way to get around most issues with outdated Safari. I have seen
no evidence in any of my two running G4 Macs (10.5.8) of adware or malware.
This is the main page TenFourFox browser for PPC Mac ; note G5 edition link:
http://www.floodgap.com/software/tenfourfox/
And if still running 10.5.6, get the Combo update to 10.5.8 for Leopard.
For Safari in later macs, there are suggestions in following article about adware
and some of that may seem like malware. I've had no adware or malware in my
PowerPC G4 Macs; there may be manual instructions on how to look for bits of
suspicious content in this support page. Avoid products such as AdwareMedic
or malwarebytes antimalware for Mac because it runs in later intel Macs OS X.
• Stop pop-up ads and adware in Safari - Apple Support
Phony "tech support" / "ransomware" popups and web pages
How to install adware - or avoid it.
Manual methods for malware, adware, performance issues may still be here:
http://www.thesafemac.com/tech-guides/
Good luck & happy computing! 🙂
{PS: this thread has been relocated to vintage PPC iMac from Intel iMac section by hosts}