Google displays whatever ads it thinks are appropriate based on the content of your website. There is no way to influence what Google chooses since it is doing it all automatically. If you are seeing "fix mirc.exe" ads, then a company has most likely decided to advertise with Google using those key words. I've also seen other adds that use "mIRC" as a keyword to advertise dating, anti-virus software, gaming, chat sites, and so on. These seem fine to me.