You are probably dealing with virus' kin; malware. These programs can infect your computer from numerous sources, including: compromised websites, software downloads bundled with adware, and previous viral infestation. Unfortunately, there is no easy solution to a malware infection as it is often accompanied by viral infection. The first thing to do is to install and run an anti-virus program such as Sophos anti-virus. Next, download and install an anti-spyware/anti-malware program. The U of A has also licensed CounterSpy for free use by faculty, staff and students. For machines not owned by the U of A, you may also want to look at SpyBot, and Ad-Aware.
These programs are often able to remove all software from your computer, but they are not always successful and they do not remove viruses. If the problem persists after disinfection, please contact your department's technical support personel.