Browser hijacked

Hi all,

After a short diagnostic bij the apple online support, a software technician told me that my browser has been hijacked. I have recently received a bunch of pop up ads. Another problem is dat every time I click on a link of a website, it will open a random (ads) websites on a new tab. Very annoying and it makes my computer run very slow. Every now and then, the browser will jam and I need to restart safari.

Anyone has experience on this problem? I had a mackeeper installed till recently, but ever since I removed it, I got these problems. If I need to install an antivirus, which one I should get?

Regards,

Ferry