New threats are emerging every day, and it is quite possible for a trojan to get into your system undetected since no corresponding definition yet exists in the virus database and the malware has not done anything suspicious to expose itself. As a result, the file monitor SpIDer Guard, which scans files, whenever they are being opened, launched, or modified, and watches over running processes, cannot detect it.
Dr.Web recommends
Schedule regular system scans to occur at least once a week. You can set up the scans to be run at the most convenient time for you—for example, when you are not using your PC.