These tools, selected by PC World’s editors, many of them free, can stop virus attacks, help you clean up problems caused by malware, and help you investigate odd behavior by your PC.

TrueCrypt
This free, Open Source encryption program lets you place files and folders in “safes” of any size.

Comodo Firewall Pro
This free firewall received top ratings for stopping unwanted outbound connections.

ThreatFire (formerly Cyberhawk)
Protect your PC against rootkits, zero-days exploits, and other threats — without interfering with your anti-virus software.

McAfee Rootkit Detective
Dig up hard-to-find rootkits with this powerful security application.

Secunia PSI Beta
Identify program security leaks and batten down the hatches with this free software.