Better safe than sorry: a PC protection mantra that most of us live by. But sometimes, despite our best efforts, a virus, trojan or any other malware does slip in. Quite often they ply their trade unobtrusively, remaining undetected by installed security products, and the only hint one has is erratic system behaviour — such as a general system slowdown, slower Internet and so on. What now?

Online virus scanners can prove to be invaluable if you suspect your PC is infected but your anti-virus application is not picking anything up. Many of the big names in the computer security business offer solutions of this sort, thus allowing users to scan their computers without installing a full-fledged anti-virus package. Mostly, using these services is as simple as downloading a small program on to your computer, activating it, and sitting back with fingers crossed while it scans.

Housecall: It’s from Trend Micro (Housecall.trend­micro.com) and is one of the few that offers detection as well as repair of malware. It can detect viruses, worms, Trojans, rootkits, spyware and more. You will need to download a small utility (make sure you get the right one, depending on whether you are using 32-bit or 64-bit Windows) that will perform the actual scanning.

There are options for full system scan, custom scan and quick scan. Housecall can scan critical system areas. It is a standalone and browser-independent process, and while detection rates are not reputed to be the best, this is still highly recommended if you are looking for removal options that your installed anti-virus is not able to provide.

BitDefender: It also has an online anti-virus tool (Bitdefender.com). It detects different kinds of malware, including spyware. BitDefender Online Scanner will scan your computer from a browser window, and if threats are detected, they will be removed. It thoroughly scans all files and folders, boot sectors and system memory, and you may set the scanner’s options to automatically cleaning any detected infections. Unlike Housecall, which asks to download a new version each time you return to the site to scan, BitDefender’s virus signatures are automatically updated each time it is launched.

Kaspersky Scanner: Have your doubts about a file you downloaded from the Net or something that was sent to you by email? Check out the online Kaspersky File Scanner (Kaspersky.com/scanforvirus) service. Indicate the path to the suspected file and it will be uploaded to the Kaspersky Lab servers where it will come under the microscope. There is a limit of 1 MB on files uploaded, though files bigger than that may be zipped (to under 1 MB). While this is known to give good results, it is a detection-only service; in other words, if a threat is found, it will not be removed. Kaspersky is currently working on a new, improved version of their online scanner. Check at Kaspersky.com/virusscanner.

Not all online scanners offer virus removal; most only offer detection. Read the small print carefully before you decide on which one to use. Also, online scanning might be a great fall-back option, but it is by no means a replacement for an installed and updated resident scanner. As Windows users, one is always open to threats where there can be no shortcuts on the security front.

Payal Dhar is a freelance technology writer