What version of Virtualbox are you running..??, look under "Help > About"
I'm running 5.0.10 r104061
I just checked what updates are available, but I did not install.
There are no updates for Version 5.0.10, but there are 3 for Version-4.
19 : Name: virtualbox-guest-x11 INSTALLED: 4.3.10-dfsg-1ubuntu5 AVAILABLE: 4.3.34-dfsg-1+deb8u1ubuntu1.14.04.1
20 : Name: virtualbox-guest-utils INSTALLED: 4.3.10-dfsg-1ubuntu5 AVAILABLE: 4.3.34-dfsg-1+deb8u1ubuntu1.14.04.1
21 : Name: virtualbox-guest-dkms INSTALLED: 4.3.10-dfsg-1ubuntu5 AVAILABLE: 4.3.34-dfsg-1+deb8u1ubuntu1.14.04.1
I checked in synaptic, I only have a "green dot" installed for Virtualbox-5.0 ,
So why is it offering updates for Version-4 ..??