According to this, a system restore will not work if the anti-virus deletes or quarantines a file during restoration:
During a restoration, an active antivirus program scans for infected files. If the antivirus program detects any infected files, the antivirus program tries to modify, move, or delete the infected files. If the antivirus program successfully cleans the infected files, System Restore restores the cleaned files. However, if the antivirus software cannot clean a file, the antivirus software deletes or quarantines the file. As a result, the restoration does not work because these actions to the file cause an inconsistent restoration state. As a result, System Restore reverts to the state immediately before the restoration.
As they have an updated ESET installed, which I know will kill the virus (because it cleaned the virus from a second computer), I'm not worried about a reoccurrance.