Q: Please Help

Remove the BitDefender package, per the vendor's instructions.   If you paid for it, request a refund.

OS X has Gatekeeper and XProtect, which — when set to the Mac App Store and identified developers via the Security & Privacy general settings — does decently well at keeping junk out.   But every time you enter your administrative password, you're granting full access to the package.

Have backups, too.  More than a few folks will never get malware, but all disks and all computers will eventually and inevitably fail.   Some will get damaged or stolen, too.    With no backups, that means data loss.

There's a belief among some folks that add-on anti-virus and anti-malware does something useful.   Among others, that it can and does cause problems and instability.    Unfortunately for your case, the anti-virus was disruptive.  Even when the packages are working correctly, it is difficult to distinguish anti-virus and anti-malware from malware given how both tend to insinuate themselves deeply into the operating system, too.    That means that subtle changes to the applications or network or the operating system can cause problems.    In the general case (and per one of the providers), anti-virus is not particularly effective, too.

Bitdefender uninstall

I'm going to assume you had no backup prior to the installation and/or other reasons for not reverting to those backups.

Either the vendor instructions were not followed, or the vendor instructions were incomplete or erroneous, or what was installed really wasn't BitDefender.  

If this really was BitDefender that was installed, then please ask the BitDefender folks for assistance.

if this wasn't downloaded from the BitDefender site, then it's quite possibly malware.

Check your network settings, and make sure your DNS server setting and your gateway router setting are as needed for your local network.

Boot into Safe Mode and see if the problem persists there.  See if you can access these and other sites in Safe Mode.

Then reboot normally, and try access again.

If that works, then it's likely something getting loaded at boot or something starting when you log in.

Here's the general sequence for adware removal which will provide some general details on how some of adware and malware packages work, but you're going to have to figure out what this package did, or generate some backups and reinstall.