Malware detection question

Recently, my Mozilla browser started opening up unwanted tab sessions. It kept occurring at such a fast rate that I couldn't close out the tabs or browser itself so I had to reboot the laptop.

My computer is already running avast! Antivirus and SuperAntiSpyware Professional edition, with negative findings after updates and scans from each.

I was concerned so I downloaded Microsoft Security Essentials (before I knew how slow it runs).

When I ran it, it discovered two items:

TrojanDownloader:Java/OpenConnection.OS
Exploit:Java/CVE-2010-0840.DR

First, how do I know these are legitimate malware items?

Second, I know no software can detect everything 100% of the time, but I'm surprised at least one of these programs didn't detect these two items, if they are real.

Third, could these two items be the cause of the tabs opening up on my Mozilla browser?

 

thanks Tim. I think the avast AntiVirus sandbox caught it and it appears to not have infected my computer. I reran the scans with the programs as well as Panda Cloud Antivirus and Windows Defender and all of them came up clean.