what is the best free antivirus for mac ox iBookG4?

Strictly speaking you don't need any, but read on:

There are many forms of ‘Malware’ that can affect a computer system, of which ‘a virus’ is but one type, ‘trojans’ another. Using the strict definition of a computer virus, no viruses that can attack OS X have so far been detected 'in the wild', i.e. in anything other than laboratory conditions. The same is not true of other forms of malware, such as Trojans. Whilst it is a fairly safe bet that your Mac will NOT be infected by a virus, it may have other security-related problem, but more likely a technical problem unrelated to any malware threat.

You may find this User Tip on Viruses, Trojan Detection and Removal, as well as general Internet Security and Privacy, useful:

https://discussions.apple.com/docs/DOC-2435

The User Tip (which you are welcome to print out and retain for future reference) seeks to offer guidance on the main security threats and how to avoid them.

More useful information can also be found here:

http://www.reedcorner.net/mmg/

Since you don't have the protection of running an updated OS, probably Sophos.

System Requirements

http://www.sophos.com/en-us/products/free-tools/sophos-antivirus-for-mac-home-ed ition/system-requirements.aspx

Test it for a while to see if it slows you down. If it does, uninstall it. But generally good reputation.

http://openforum.sophos.com/t5/Sophos-Anti-Virus-for-Mac-Home/Removing-Sophos-An ti-Virus-for-Mac-Home-Edition/td-p/37/page/7

You can check here: http://www.adobe.com/products/flash/about/ to see which version you should install for your Mac and OS. Note that version 10,1,102,64 is the last version available to PPC Mac users*. The latest version,10.3.183.23 or later, is for Intel Macs only running Tiger or Leopard, as Adobe no longer support the PPC platform. Version 11.4.402.265 is for Snow Leopard onwards.

* Unhelpfully, if you want the last version for PPC Macs, you need to go here: http://kb2.adobe.com/cps/142/tn_14266.html and scroll down to 'Archived Versions/Older Archives'. Flash Player 10.1.102.64 is the one you download. More information here: http://kb2.adobe.com/cps/838/cpsid_83808.html

You should first uninstall any previous version of Flash Player, using the uninstaller from here (make sure you use the correct one!):

http://kb2.adobe.com/cps/909/cpsid_90906.html

and also that you follow the instructions closely, such as closing ALL applications first before installing. You must also carry out a permission repair after installing anything from Adobe.

(If you are running a PPC Mac with Flash Player 10.1.102.64 and are having problems with watching videos on FaceBook or other sites, try the following solution which fools the site into thinking that you are running the version 11.5.502.55:)

Download this http://scriptogr.am/nordkril/post/adobe-flash-11.5-for-powerpc to your desktop, unzip it, and replace the current Flash Player plug-in which is in your main/Library/Internet Plug-Ins folder, (not the user Library). Save the old one just in case this one doesn't work.

Any older version of Flash you run, including anything that "tricks" a site into thinking you have a newer version, will be inherently VERY unsafe. If you use Safari, get clicktoflash or Firefox, get Flashblock. These will set placeholder icons for any Flash content. You click on the placeholder to allow Flash to run. I would be extremely careful where I allow Flash to run. Myself, I wouldn't run it at all from such an old version.

Any older version of Flash you run, including anything that "tricks" a site into thinking you have a newer version, will be inherently VERY unsafe.

Not strictly true, particularly for PPC Macs, but yes, ClickToFlash is a good add-on.

Why not? You think there aren't any PPC Flash exploits?

http://www.adobe.com/support/security/#flashplayer

And TenFourFox has all plugins disabled by default, since they're not considered safe.

Message was edited by: WZZZ

None have so far been recorded for any version of PPC Macs running Leopard or below. None of the security alerts from Adobe mention any version of Flash Player that can run on a PPC Mac.

While no one may be bothering to write exploits in PPC code any longer, at least for Flash, that doesn't mean that there aren't any still floating around. The following doesn't specifically mention PPC/Intel, but that doesn't mean there weren't critical vulnerabilities being exploited for PPC in 10.1.102.64. I wouldn't want to take the chance.

Critical vulnerabilities have been identified in Adobe Flash Player 10.1.102.64 and earlier versions for Windows, Macintosh, Linux, and Solaris. These vulnerabilities could cause the application to crash and could potentially allow an attacker to take control of the affected system.

http://www.adobe.com/support/security/bulletins/apsb11-02.html

And, from TenFourFox

PowerPC plugins are unmaintained and insecure, and Mozilla is changing the plugin environment

No major plugin is being maintained for Power Macs any more: Flash stopped updates with Flash 10.1.102.64 in November 2010, and QuickTime 7 for the PowerPC was decommissioned with the release of QuickTime 7.7 and OS X Lion in August 2011. (Tiger users have not had an update since QT 7.6.4 in September 2009.)

Plugins have special access to the system. When they are instantiated by the browser, they run as if you were running any regular application, which is true even for out-of-process plugins (which were never available for 10.4Fx due to Tiger SDK limitations). Like any buggy or insecure application, they can be exploited or made to crash, and because the plugin runs within the browser, such methods can also be used to attack, spy upon or destabilize the browser as well. They have also been used to attack the network the computer is running on, and a well-crafted attack vector such as that example can run anywhere Flash does, including Power Macs. Because plugins load automatically by default when the page calls for them, your system could be exploited before you even notice.

Many of these attacks can be mitigated, though not entirely prevented, by the use of add-ons that can block plugins from loading. However, there is still another problem apart from security: Mozilla is changing the environment and the technical requirements for how plugins interact with the system. These technical requirements are difficult to achieve with Mac OS X 10.4, and there are known graphical and compatibility bugs already. It is entirely possible that in the near future, extant PPC-compatible plugins will not function properly or at all.

http://code.google.com/p/tenfourfox/wiki/PluginsNoLongerSupported

Message was edited by: WZZZ

Largely irrelavent as Firefox is not available for, and does not support, the PPC platform.

It is easy to allow TenFourFox to allow plug-ins.

Klaus1 wrote:

Largely irrelavent as Firefox is not available for, and does not support, the PPC platform.

It is easy to allow TenFourFox to allow plug-ins.

That's neither here nor there. The essential idea is that running this older version of Flash, PPC or not, is inherently risky.

You really love having the last word don't you? 😀

Even when it is irrelavant and imaterial.

You haven't proved your assertion with any evidence whatsoever. Show me that and you can have the last word. Otherwise, you are posting possibly dangerous information for others to come along and see.

None have so far been recorded for any version of PPC Macs running Leopard or below.

That's just your word. Back that up.

None of the security alerts from Adobe mention any version of Flash Player that can run on a PPC Mac.

The quote and link I provided above for the critical update from Adobe for the latest version that a PPC Mac can run do not explicitly exclude or include PPC.

Show me where PPC is excluded from that.

http://www.adobe.com/support/security/bulletins/apsb11-02.html