Trust me, if there was a major hack that is blockchain.info's fault then everyone would have been affected and everyone would be complaining by now. But the fact that it's just you apparently seem to suggest that it's definitely something on your side.

Firstly, check whether your transactions actually show up. If not then it's probably a problem with syncing with blockchain.info servers, your balance isn't lost.

If you can see the outgoing transaction then post it here. There is a very slight chance we can trace where it went to.

Remember that antivirus scans are not always conclusive. I've stored thousands with blockchain.info in the past before they switched to the new version, without any issues.