I have TrendMicro PC Cillian 2005 and I love it. It has never slowed my computer down. I'm on my third Internet Security Suite in a year and half, and I wish I had a package like this to start with, instead of McAffee or Norton. What a waste of money.
I think you may have some spyware/adaware and or trojans/worms, because PC Cillian wouldn't do that.
A lot of people don't realize an security suite alone is not going to keep all that crap off your machine. It is not designed for Trojans, Worms, Rootkit Malware, etc. You need a good Spyware, Adaware program as well.
There is a site www.diamondcs.com that offers some software called ProcessGuard, WormGuard, PortExplorer, Trojan Defense Suite-3 or TDS-3, and believe me, they are true to there word, nothing will get in your computer unless you allow it. Check it out! There prices are so reasonable, I was surprised. I don't know I done with out it, (I kept reformatting my computer).
Now that I have the programs from www.diamondcs.com(four of them) and my PC Cillian 2005, Microsoft AntiSpyware, Adaware SE Pro with v1.05 build, and of course Acronis True Image 8.0 to image my drive(s), I don't have to worry about anything unless I'm stupid and click on something I shouldn't have.
I think that these programs are a small price to pay in order to keep a safe and secure computer, and not to worry!