I'm using the Zirona plugin too. The more I look at this, the more it looks like there's been some confusion here.
The current version on zirona.com is 2.0. At http://wordpress.org/extend/plugins/advanced-search-plugin/ it says:
It is safe to update to the final version of this plugin (version 3.0). We strongly suggest you either update to this version or delete the plugin.
The link offered downloads a plugin that has nothing in it apart from a warning that the plugin isn't safe!
As far as I can tell the malware plugin here either (1) has nothing to do with the Zirona version, or (2) is a malicious fork of the Zirona plugin. Either way, if you have the Zirona plugin installed your plugin page tells you there's an upgrade available, which downloads the empty plugin with the warning.
While I'm pretty sure there's been a mix-up here, it's hard to be sure, and with malware involved, what choice is there but to err on the safe side and revert to the standard WP search?
(Another topic, but really, if the WP core search improved even a little bit, we wouldn't be having this discussion ;-)