Network / Sharing :: Browser Download Speed Suddenly Reduced / Browsing Is Normal

I have a 600Kbits per sc connection, cable modem so my downloading speed is around 60-70 kbytes/s same in utorrent and in browser downloads, i use windows 8.1 pro, 64 bits, recently my google chrome was turning slow and firefox too, i dunno if my pc was infected by viruses. i scanned wit havast and bitdefender free versions and found nothing.and yesterday when i tried to download a pdf file, i dunno why nut download speed was horrible, started with 24 and then it was like 3-4 kbytes/s and it even failed later.

I thought it was a connection problem so i restarted my connection, browsing was fine everything except downloading seemed okay.

I tried doing the same things with different browsers like firefox or internet explorer but the problem was same.

When i tried utorrent, it was perfectly normal, it gave the usual download speed of 60-70 kbytes/s so it seems the problem was onl in downloading with browsers and no problem with browsing and utorrent. I hard resetted my pc and reinstalled fresh copy of win 8.1 but again twas the same.did it 3 times already but no change. I dunno if it is a virus or something but i am exhausted, ( before formatting my pc , i backed up my files in an external hdd so it may be possible that if there is a virus involved then it may have came back due to my external hdd)

I checked Speedtest.net by Ookla - The Global Broadband Speed Test and there too, showed 0.56 mbps , so it was normal there too