These protect to a great extent, but are best at a full scan of your hard drive after it has been infected.
Free antivirus program for Windows and Mac; add-ons and upgrades available.
Spybot Search and Destroy:
Windows program against Malware and Spyware; home and business use.
Malware Bytes Anti-Malware:
For home or business, Mac or Windows; Android mobile app also available to fight against Malware and Spyware.
Some of the best things in life are free.
Physical security, such as locking your office, car or apartment door is free. Critically evaluating potential "social engineering" requests you get for personal information via email, phone calls or even directly from friends - is free. Taking your laptop with you when you leave your study table at the Library for lunch is also free.
Other aspects of physical security require a modest investment, such as buying a secure or encrypted USB drive on which to store your school work and private information. Consider this investment in light of how many hours you devoted to composing your term projects.
Did you know that every time you log into Gmail or Facebook, a copy of your contacts and friends list is left behind when you log out? Did you know it is possible to set up an email client, such as Mozilla's Thunderbird, from a USB drive so that no personal information is left behind on whatever computer you use?
The inconvenience you incur by de-selecting the option on Gmail and Facebook to "LEAVE ME LOGGED IN" or activating the geo-location feature on your phone only when you need it - is also free.
The greater level of personal privacy and freedom from aggressive marketing and potential loss of personal information - PRICELESS!
Be wary of hyperlinks and email attachments.
Never give out your personal information when it is requested via email. Your bank, credit card company, employer, college, etc. already know that stuff so why would they ask you to provide it?
Keep your anti-virus software up to date.