Lately, some visits to Zippyshare to download files will go direct to the download page and then divert to another browser tab to some unexpected webpage. This is known as a "Browser Redirect" of Browser Hijack". This appears to be initiating at Zippyshare rather than from anything on your computer or browser and it only happens intermittently. Under no circumstances should you do anything on this unwanted webpage. My experience is that you are likely to be able to close the particular tab or click on the Zippyshare tab and do your download as normal with no effect. Failing that, close your browser and start again.
The last two I have seen is to the effect that my Adobe Flash Player is out-of-date with an overlay panel asking me to click "OK" to start the update. To do so would be foolish and will surely result in something totally unwanted on my computer. Other pages will tell you that you have lots of viruses, spyware, outdated drivers and so on. Usually these are seeking to scare you into buying a piece of useless or dangerous software. Regardless, do not click anywhere within these pages.
There are also browser hijackers which manage to insert add-ons into browsers for browser redirection or take over search functions, bars etc. This certainly does not appear to be what is happening here.
I am looking into the possibility of moving to another host for my files and I will let you know. In the meantime, be careful.