To quote the Onspeed website

"ONSPEED is a software download which utilises a unique 9 patent approved compression technology that increases your existing Internet connection speed by up to 5 times...

...the ONSPEED software redirects that request to the ONSPEED Compression Servers. They take the respective Web Page content, compresses it and sends it back down to the ONSPEED software which decompresses it and sends it to the Browser requesting the information."

Blah blah blah. Anyway, it's been a pain in the **** ever since I downloaded it but it does speed up my connection a bit so I've stuck with it.