No need to purchase Secure Clean. Ccleaner does the same thing for free. It will clean temporary files, logs and cookies. Has other functions as well.
Would suggest you also get a firewall other than Windows firewall. There are a few very good firewalls for free.
Most malware such as Spydawn require some action by the user to get installed on your computer. Such as clicking on links in IM's, emails or websites and opening email attachments. There are sites on the web where you can get infected by just visiting them. Those are known as drivebys. Downloading free screensavers or using P2P programs to download from unknown sources are two other ways that you get infected.http://www.ccleaner.com/
Below is a link to a list of free software products such as firewallshttp://www.bleepingcomputer.com/forums/topic3616.html
To avoid a lot of malware, installing another browser such as Firefox with NoScript extension will prevent driveby infections.