I have a querie about a possible bad file avast has found on my new mac,it did a full scan and came up with 1 warning error 42110 and said the file is a decompression bomb,obviously im new to mac and im bamboozled,have i got a virus or a bad file already

Great advice, there, sam.

Here's another good source of information for you, being a switcher:

http://www.apple.com/support/switch101

Am i right in thinking not to have any AV programs whatsoever then?

Other than what's built in to the Mac OS, yes.

im also about to disable java.Is that right?

Yes, unless you need it, which you probably don't.

clamAV isnt commercial am i right?, whats the difference?

ClamXav is not an intrusive system modification, and it's not developed by scam artists. You don't need it unless you want to be able to detect Windows malware in files you exchange with others. I myself have never seen Windows malware that wasn't instantly recognizable for what it was, but if you feel the need for something to help you make that determination, use ClamXav. Bye now.

Sam, be sure to read the article link in my response, above, OK? It will help you with a lot of things.

Also, here's another response from another helper:

For me "bootroot.loader" appears as a plain document, both on Lion and ML. So the bootroot.loader seems to be necessary and cannot be simply removed. The corrupted file should be replaced by the original, maybe from a TM backup, if it is really corrupted and not only an illusion produced by the AV software?

I'm pretty sure it was a error on Avast's part. But if you every do have any "explosion" on your Mac, revisit this.

All the best.

I just checked a forum thread on Avast's own site. Here's some clips (Linc is correct).

42110 means "decompression bomb", and the package simply reached the limit where it has suspiciously high compression ratio. It's fair to warn about this (some malware programs used decompression bombs to overload antivirus processing), but in few cases this might be natural consequience of highly "packable" content. dmg might be the case.

A higher level tech support says "Yep, that's native to the OS. Don't delete it."

So yeah, if anyone else needs to know, mediakit.framework is part of the OS (Mac OS X 10.5., and so is bootroot.loader.dmg. They are supposed to be there...

Thanks, Kurt!