In my opinion, there's no possible way the image of Ubuntu you downloaded from the internet could have been modified by a compromised Windows installation in such a way that by booting it your actions on the running system could be tracked (unless you downloaded a fishy Ubuntu image in first place); how specific the malicious software running on the Windows installation should have been to do such a thing?
In any case, you can check whether your Ubuntu DVD is exactly how it's meant to be by running md5sum /dev/sr0
and by comparing the output value with the MD5 sum of the original image found here (sr0
might vary based on your configuration if you have more than one drive; you may check the full list of DVD drives by running lsblk
);
You can check whether someone is "hacking" your wireless network by looking at the list of the connected hosts in the router's settings, as most routers provide such a list; if the only IP addresses showing up are from known hosts, such as your PC, then no one is "hacking" your wireless network;
Tl;dr
Your connection is probably slow for other reasons; I'd rule out an hardware problem because in that case the slowness would probably be persistent rather than intermittent like you're describing:
when using the internet, make sure that you're close enough to the router; avoid using the wifi in places which require the signal to go through bearing walls; in my experience, even adverse atmospheric conditions may play a role, e.g. if the signal has to go through the rain;
other than that, it's probably your ISP's fault, which might be arbitrarily reducing the speed of the connection during certain time slots, or simply sometimes the traffic at the ISP's central to is too huge that the central can't handle it, resulting in the slow speed.