hello people i wanted to know what effect does an antivirus have on the surfing speed or the download speed?? i am thinking of installing one but have experienced slow speeds compared to surfing without an antivirus…if it slows down to some extent….why does it? thank you

do u think kaspersky was a good choice for an antivirus? should i change it?
is it still effective eventhough there is a newer version out already?
does kaspersky antivirus v6 protect the PC from other malicious programs like adware, spyware and the like or it only protects the computer from viruses? cos i downloaded spyware doctor, should i just unintstall spyware doc.?