Spyware are pieces of software code, which reside in your computer and keep a track of your activities. This is why they are called spy-ware, software that spies on your system and records your activities.
These malicious software can store information about your bank and credit card information, your online transactions, Internet browsing history (the sites that you visit), email addresses in your contact lists and other personal and sensitive data. It can create copies of your images or video files, duplicate your emails and send emails to your contact address book using your own email address or use your email account to send spam to other unsuspecting users, who will treat these emails as coming from you.
Spyware can be used for various purposes, from showing targeted ads to you, to misappropriating your money using your financial details. It is also used to create a ‘bot-net‘, the latest way to send spam. The Spyware on your system will use your computer as a server to send mails. Since your computer is not a regular spammer, the mails will be treated as genuine and will be delivered to the recipients inbox, instead of the spam folder.
To see if your computer is infected or not, scan it regularly with a good anti-Spyware. You can try the FREE SCAN available HERE